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      HashiCorp

      Use HashiCorp Vault to Manage Secrets


      Updated by Linode Contributed by Linode

      HashiCorp Vault is a secrets management tool that helps to provide secure, automated access to sensitive data. Vault meets these use cases by coupling authentication methods (such as application tokens) to secret engines (such as simple key/value pairs) using policies to control how access is granted. In this guide, you will install, configure, and access Vault in an example deployment to illustrate Vault’s features and API.

      This guide will use the latest version of Vault, which is 1.1.0 at the time of this writing.

      Why Use Vault?

      A service such as Vault requires operational effort to run securely and effectively. Given the added complexity of using Vault as part of an application, in what way does it add value?

      Consider a simple application that must use an API token or other secret value. How should this sensitive credential be given to the application at runtime?

      • Committing the secret alongside the rest of the application code in a version control system such as git is a poor security practice for a number of reasons, including that the sensitive value is recorded in plaintext and not protected in any way.
      • Recording a secret in a file that is passed to an application requires that the file be securely populated in the first place and strictly access-controlled.
      • Static credentials are challenging to rotate or restrict access to if an application is compromised.

      Vault solves these and other problems in a number of ways, including:

      • Services and applications that run without operator interaction can authenticate to Vault using values that can be rotated, revoked, and permission-controlled.
      • Some secrets engines can generate temporary, dynamically-generated secrets to ensure that credentials expire after a period of time.
      • Policies for users and machine accounts can be strictly controlled for specific types of access to particular paths.

      Concepts

      Before continuing, you should familiarize yourself with important Vault terms and concepts that will be used later in this guide.

      • A token is the the underlying mechanism that underpins access to Vault resources. Whether a user authenticates to Vault using a GitHub token or an application-driven service authenticates using an AppRole RoleID and SecretID, all forms of authentication are eventually normalized to a token. Tokens are typically short-lived (that is, expire after a period or time-to-live, or ttl) and have one or more policies attached to them.
      • A Vault policy dictates certain actions that may be performed upon a Vault path. Capabilities such as the ability to read a secret, write secrets, and delete them are all examples of actions that are defined in a policy for a particular path.
      • A path in Vault is similar in form to a Unix filesystem path (like /etc) or a URL (such as /blog/title). Users and machine accounts interact with Vault over particular paths in order to retrieve secrets, change settings, or otherwise interact with a running Vault service. All Vault access is performed over a REST interface, so these paths eventually take the form of an HTTP URL. While some paths interact with the Vault service itself to manage resources such as policies or settings, many paths serve as an endpoint to either authenticate to Vault or interact with a secret engine.
      • A secret engine is a backend used in Vault to provide secrets to Vault users. The simplest example of a secret engine is the key/value backend, which simply returns plain text values that may be stored at particular paths (these secrets remain encrypted on the backend). Other examples of secret backends include the PKI backend, which can generate and manage TLS certificates, and the TOTP backend, which can generate temporary one-time passwords for web sites that require multi-factor authentication (including the Linode Manager).

      Installation

      This guide will setup Vault in a simple, local filesystem-only configuration. The steps listed here apply equally to any distribution.

      These installation steps will:

      • Procure a TLS certificate to ensure that all communications between Vault and clients are encrypted.
      • Configure Vault for local filesystem storage.
      • Install the vault binary and set up the operating system to operate Vault as a service.

      Note

      The configuration outlined in this guide is suitable for small deployments. In situations that call for highly-available or fault-tolerant services, consider running more than one Vault instance with a highly-available storage backend such as Consul.

      Before you Begin

      1. Familiarize yourself with Linode’s Getting Started guide and complete the steps for deploying and setting up a Linode running a recent Linux distribution (such as Ubuntu 18.04 or CentOS 7), including setting the hostname and timezone.

        Note

        Setting the full hostname correctly in /etc/hosts is important in this guide in order to terminate TLS on Vault correctly. Your Linode’s fully qualified domain name and short hostname should be present in the /etc/hosts file before continuing.

      2. This guide uses sudo wherever possible. Complete the sections of our Securing Your Server guide to create a standard user account, harden SSH access, and remove unnecessary network services.

      3. Follow our UFW Guide in order to install and configure a firewall on your Ubuntu or Debian-based system, or our FirewallD Guide for rpm or CentOS-based systems. Consider reviewing Vault’s Production Hardening recommendations if this will be used in a production environment.

        Note

        When configuring a firewall, keep in mind that Vault listens on port 8200 by default and Let’s Encrypt utilizes ports 80 (HTTP) and 443 (HTTPS).

      4. Ensure your system is up to date. On Debian-based systems, use:

        sudo apt update && sudo apt upgrade
        

        While on rpm-based systems, such as CentOS, use:

        sudo yum update
        

      Acquire a TLS Certificate

      1. Follow the steps in our Secure HTTP Traffic with Certbot guide to acquire a TLS certificate.

      2. Add a system group in order to grant limited read access to the TLS files created by Certbot.

        sudo groupadd tls
        
      3. Change the group ownership of certificate files in the Let’s Encrypt directory to tls.

        sudo chgrp -R tls /etc/letsencrypt/{archive,live}
        
      4. Grant members of the tls group read access to the necessary directories and files.

        sudo chmod g+rx /etc/letsencrypt/{archive,live}
        sudo find /etc/letsencrypt/archive -name 'privkey*' -exec chmod g+r {} ';'
        

      Download Vault files

      1. Download the release binary for Vault.

        wget https://releases.hashicorp.com/vault/1.1.0/vault_1.1.0_linux_amd64.zip
        

        Note

        If you receive an error that indicates wget is missing from your system, install the wget package and try again.

      2. Download the checksum file, which will verify that the zip file is not corrupt.

        wget https://releases.hashicorp.com/vault/1.1.0/vault_1.1.0_SHA256SUMS
        
      3. Download the checksum signature file, which verifies that the checksum file has not been tampered with.

        wget https://releases.hashicorp.com/vault/1.1.0/vault_1.1.0_SHA256SUMS.sig
        

      Verify the Downloads

      1. Import the HashiCorp Security GPG key (listed on the HashiCorp Security page under Secure Communications):

        gpg --recv-keys 51852D87348FFC4C
        

        The output should show that the key was imported:

          
        gpg: /home/user/.gnupg/trustdb.gpg: trustdb created
        gpg: key 51852D87348FFC4C: public key "HashiCorp Security " imported
        gpg: no ultimately trusted keys found
        gpg: Total number processed: 1
        gpg:               imported: 1
        
        

        Note

        If an error occurs with the error message keyserver receive failed: Syntax error in URI, simply try rerunning the gpg command again.

        Note

        If you receive errors that indicate the dirmngr software is missing or inaccessible, install dirmngr using your package manager and run the GPG command again.

      2. Verify the checksum file’s GPG signature:

        gpg --verify vault*.sig vault*SHA256SUMS
        

        The output should contain the Good signature from "HashiCorp Security <security@hashicorp.com>" confirmation message:

          
        gpg: Signature made Mon 18 Mar 2019 01:44:51 PM MDT
        gpg:                using RSA key 91A6E7F85D05C65630BEF18951852D87348FFC4C
        gpg: Good signature from "HashiCorp Security <security@hashicorp.com>" [unknown]
        gpg: WARNING: This key is not certified with a trusted signature!
        gpg:          There is no indication that the signature belongs to the owner.
        Primary key fingerprint: 91A6 E7F8 5D05 C656 30BE  F189 5185 2D87 348F FC4C
        
        
      3. Verify that the fingerprint output matches the fingerprint listed in the Secure Communications section of the HashiCorp Security page.

      4. Verify the .zip archive’s checksum:

        sha256sum -c vault*SHA256SUMS 2>&1 | grep OK
        

        The output should show the file’s name as given in the vault*SHA256SUMS file:

          
        vault_1.1.0_linux_amd64.zip: OK
        
        

      Install the Vault Executable

      1. Extract the Vault executable to the local directory.

        unzip vault_*_linux_amd64.zip
        

        Note

        If you receive an error that indicates unzip is missing from your system, install the unzip package and try again.

      2. Move the vault executable into a system-wide location.

        sudo mv vault /usr/local/bin
        
      3. Reset the ownership and permissions on the executable.

        sudo chown root:root /usr/local/bin/vault
        sudo chmod 755 /usr/local/bin/vault
        
      4. Set executable capabilities on the vault binary. This will grant Vault privileges to lock memory, which is a best practice for running Vault securely (see the Vault documentation for additional information).

        sudo setcap cap_ipc_lock=+ep /usr/local/bin/vault
        
      5. Verify that vault is now available in the local shell.

        vault --version
        

        The output of this command should return the following.

          
        Vault v1.1.0 ('36aa8c8dd1936e10ebd7a4c1d412ae0e6f7900bd')
        
        

      System Vault Configuration

      1. Create a system user that vault will run as when the service is started.

        sudo useradd --system -d /etc/vault.d -s /bin/nologin vault
        
      2. Add the vault user to the previously created tls group, which will grant the user the ability to read Let’s Encrypt certificates.

        sudo gpasswd -a vault tls
        
      3. Create the data directory and configuration directory for vault with limited permissions.

        sudo install -o vault -g vault -m 750 -d /var/lib/vault
        sudo install -o vault -g vault -m 750 -d /etc/vault.d
        
      4. Create a systemd service file that will control how to run vault persistently as a system daemon.

        /etc/systemd/system/vault.service
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        [Unit]
        Description="a tool for managing secrets"
        Documentation=https://www.vaultproject.io/docs/
        Requires=network-online.target
        After=network-online.target
        ConditionFileNotEmpty=/etc/vault.d/vault.hcl
        
        [Service]
        User=vault
        Group=vault
        ProtectSystem=full
        ProtectHome=read-only
        PrivateTmp=yes
        PrivateDevices=yes
        SecureBits=keep-caps
        AmbientCapabilities=CAP_IPC_LOCK
        Capabilities=CAP_IPC_LOCK+ep
        CapabilityBoundingSet=CAP_SYSLOG CAP_IPC_LOCK
        NoNewPrivileges=yes
        ExecStart=/usr/local/bin/vault server -config=/etc/vault.d/vault.hcl
        ExecReload=/bin/kill --signal HUP $MAINPID
        KillMode=process
        KillSignal=SIGINT
        Restart=on-failure
        RestartSec=5
        TimeoutStopSec=30
        StartLimitIntervalSec=60
        StartLimitBurst=3
        LimitNOFILE=65536
        
        [Install]
        WantedBy=multi-user.target

        These systemd service options define a number of important settings to ensure that Vault runs securely and reliably. Review the Vault documentation for a complete explanation of what these options achieve.

      Configuration

      Configure Vault

      1. Create a configuration file for Vault with the following contents, replacing example.com with the domain used in your Let’s Encrypt certificates.

        /etc/vault.d/vault.hcl
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        listener "tcp" {
          address = "0.0.0.0:8200"
          tls_cert_file = "/etc/letsencrypt/live/example.com/fullchain.pem"
          tls_key_file = "/etc/letsencrypt/live/example.com/privkey.pem"
        }
        
        storage "file" {
          path = "/var/lib/vault"
        }

        This configuration will use the Let’s Encrypt certificates created in the previous steps to terminate TLS for the Vault service. This ensures that secrets will never be transmitted in plaintext. The actual storage for Vault will be on the local filesystem at /var/lib/vault.

      Run The Vault Service

      1. Vault is now ready to run. Start the service using systemctl.

        sudo systemctl start vault
        
      2. If desired, enable the service as well so that Vault starts at system boot time.

        sudo systemctl enable vault
        
      3. Confirm that Vault is operational by using the vault executable to check for the service’s status. Set the VAULT_ADDR environment variable to https://example.com:8200, replacing example.com with your own domain:

        export VAULT_ADDR=https://example.com:8200
        
      4. vault commands should now be sent to your local Vault instance. To confirm this, run the vault status command:

        vault status
        

        The command should return output similar to the following:

          
        Key                Value
        ---                -----
        Seal Type          shamir
        Initialized        false
        Sealed             true
        Total Shares       0
        Threshold          0
        Unseal Progress    0/0
        Unseal Nonce       n/a
        Version            n/a
        HA Enabled         false
        
        

      The remainder of this tutorial assumes that the environment variable VAULT_ADDR is set to this value to ensure that requests are sent to the correct Vault host.

      Initializing Vault

      At this stage, Vault is installed and running, but not yet initialized. The following steps will initialize the Vault backend, which sets unseal keys and returns the initial root token. Initialization occurs only one time for a Vault deployment.

      There are two configurable options to choose when performing the initialization step. The first value is the number of key shares, which controls the total number of unseal keys that Vault will generate. The second value is the key threshold, which controls how many of these unseal key shares are required before Vault will successfully unseal itself. Unsealing is required whenever Vault is restarted or otherwise brought online after being in a previously offline state.

      To illustrate this concept, consider a secure server in a data center. Because the Vault database is only decrypted in-memory, stealing or bringing the server offline for any reason will leave the only copy of Vault’s database on the filesystem in encrypted form, or “sealed”.

      When starting the server again, a key share of 3 and key threshold of 2 means that 3 keys exist, but at least 2 must be provided at startup for Vault to derive its decryption key and load its database into memory for access once again.

      The key share count ensure that multiple keys can exist at different locations for a degree of fault tolerance and backup purposes. The key threshold count ensures that compromising one unseal key alone is not sufficient to decrypt Vault data.

      1. Choose a value for the number of key shares and key threshold. Your situation may vary, but as an example, consider a team of three people in charge of operating Vault. A key share of 3 ensures that each member holds one unseal key. A key threshold of 2 means that no single operator can lose their key and compromise the system or steal the Vault database without coordinating with another operator.

      2. Using these chosen values, execute the initialization command. Be prepared to save the output that is returned from the following command, as it is only viewable once.

        vault operator init -key-shares=3 -key-threshold=2
        

        This command will return output similar to the following:

          
        Unseal Key 1: BaR6GUWRY8hIeNyuzAn7FTa82DiIldgvEZhOKhVsl0X5
        Unseal Key 2: jzh7lji1NX9TsNVGycUudSIy/X4lczJgsCpRfm3m8Q03
        Unseal Key 3: JfdH8LqEyc4B+xLMBX6/LT9o8G/6isC2ZFfz+iNMIW/0
        
        Initial Root Token: s.YijNa8lqSDeho1tJBtY02983
        
        Vault initialized with 3 key shares and a key threshold of 2. Please securely
        distribute the key shares printed above. When the Vault is re-sealed,
        restarted, or stopped, you must supply at least 2 of these keys to unseal it
        before it can start servicing requests.
        
        Vault does not store the generated master key. Without at least 2 key to
        reconstruct the master key, Vault will remain permanently sealed!
        
        It is possible to generate new unseal keys, provided you have a quorum of
        existing unseal keys shares. See "vault operator rekey" for more information.
        
        
      3. In a production scenario, these unseal keys should be stored in separate locations. For example, store one in a password manager such as LastPass, encrypted one with gpg, and store another offline on a USB key. Doing so ensures that compromising one storage location is not sufficient to recover the number of unseal keys required to decrypt the Vault database.

      4. The Initial Root Token is equivalent to the “root” or superuser account for the Vault API. Record and protect this token in a similar fashion. Like the root account on a Unix system, this token should be used to create less-privileged accounts to use for day-to-day interactions with Vault and the root token should be used infrequently due to its widespread privileges.

      Unseal Vault

      After initialization, Vault will be sealed. The following unseal steps must be performed any time the vault service is brought down and then brought up again, such as when performing systemctl restart vault or restarting the host machine.

      1. With VAULT_ADDR set appropriately, execute the unseal command.

        vault operator unseal
        

        A prompt will appear:

          
        Unseal Key (will be hidden):
        
        
      2. Paste or enter one unseal key and press Enter. The command will finish with output similar to the following:

          
        Unseal Key (will be hidden):
        Key                Value
        ---                -----
        Seal Type          shamir
        Initialized        true
        Sealed             true
        Total Shares       3
        Threshold          2
        Unseal Progress    1/2
        Unseal Nonce       0124ce2a-6229-fac1-0e3f-da3e97e00583
        Version            1.1.0
        HA Enabled         false
        
        

        Notice that the output indicates that the one out of two required unseal keys have been provided.

      3. Perform the unseal command again.

        vault operator unseal
        
      4. Enter a different unseal key when the prompt appears.

          
        Unseal Key (will be hidden):
        
        
      5. The resulting output should indicate that Vault is now unsealed (notice the Sealed false line).

          
        Unseal Key (will be hidden):
        Key             Value
        ---             -----
        Seal Type       shamir
        Initialized     true
        Sealed          false
        Total Shares    3
        Threshold       2
        Version         1.1.0
        Cluster Name    vault-cluster-a397153e
        Cluster ID      a065557e-3ee8-9d26-4d90-b90c8d69fa5d
        HA Enabled      false
        
        

      Vault is now operational.

      Using Vault

      Token Authentication

      When interacting with Vault over its REST API, Vault identifies and authenticates most requests by the presence of a token. While the initial root token can be used for now, the Policies section of this guide explains how to provision additional tokens.

      1. Set the VAULT_TOKEN environment variable to the value of the previously-obtained root token. This token is the authentication mechanism that the vault command will rely on for future interaction with Vault. The actual root token will be different in your environment.

        export VAULT_TOKEN=s.YijNa8lqSDeho1tJBtY02983
        
      2. Use the token lookup subcommand to confirm that the token is valid and has the expected permissions.

        vault token lookup
        
      3. The output of this command should include the following:

          
        policies            [root]
        
        

      The KV Secret Backend

      Vault backends are the core mechanism Vault uses to permit users to read and write secret values. The simplest backend to illustrate this functionality is the KV backend. This backend lets clients write key/value pairs (such as mysecret=apikey) that can be read later.

      1. Enable the secret backend by using the enable Vault subcommand.

        vault secrets enable -version=2 kv
        
      2. Write an example value to the KV backend using the kv put Vault subcommand.

        vault kv put kv/myservice api_token=secretvalue
        

        This command should return output similar to the following:

          
        Key              Value
        ---              -----
        created_time     2019-03-31T04:35:38.631167678Z
        deletion_time    n/a
        destroyed        false
        version          1
        
        
      3. Read this value from the kv/myservice path.

        vault kv get kv/myservice
        

        This command should return output similar to the following:

          
        ====== Metadata ======
        Key              Value
        ---              -----
        created_time     2019-03-31T04:35:38.631167678Z
        deletion_time    n/a
        destroyed        false
        version          1
        
        ====== Data ======
        Key          Value
        ---          -----
        api_token    secretvalue
        
        
      4. Many utilities and script are better suited to process json output. Use the -format=json flag to do a read once more, with the results return in JSON form.

        vault kv get -format=json kv/myservice
        
        {
          "request_id": "2734ea81-6f39-c017-4c73-2719b2018b65",
          "lease_id": "",
          "lease_duration": 0,
          "renewable": false,
          "data": {
            "data": {
              "api_token": "secretvalue"
            },
            "metadata": {
              "created_time": "2019-03-31T04:35:38.631167678Z",
              "deletion_time": "",
              "destroyed": false,
              "version": 1
            }
          },
          "warnings": null
        }

      Policies

      Up until this point, we have performed API calls to Vault with the root token. Production best practices dictate that this token should rarely be used and most operations should be performed with lesser-privileged tokens associated with controlled policies.

      Policies are defined by specifying a particular path and the set of capabilities that are permitted by a user upon the path. In our previous commands, the path has been kv/myservice, so we can create a policy to only read this secret and perform no other operations, including reading or listing secrets. When no policy exists for a particular path, Vault denies operations by default.

      In the case of the KV backend, Vault distinguishes operations upon the stored data, which are the actual stored values, and metadata, which includes information such as version history. In this example, we will create a policy to control access to the key/value data alone.

      1. Create the following Vault policy file.

        policy.hcl
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        path "kv/data/myservice" {
          capabilities = ["read"]
        }

        This simple policy will permit any token associated with it to read the secret stored at the KV secret backend path kv/myservice.

      2. Load this policy into Vault using the policy write subcommand. The following command names the aforementioned policy read-myservice.

        vault policy write read-myservice policy.hcl
        
      3. To illustrate the use of this policy, create a new token with this new policy associated with it.

        vault token create -policy=read-myservice
        

        This command should return output similar to the following.

          
        Key                  Value
        ---                  -----
        token                s.YdpJWRRaEIgdOW4y72sSVygy
        token_accessor       07akQfzg0TDjj3YoZSGMPkHA
        token_duration       768h
        token_renewable      true
        token_policies       ["default" "read-myservice"]
        identity_policies    []
        policies             ["default" "read-myservice"]
        
        
      4. Open another terminal window or tab and login to the same host that Vault is running on. Set the VAULT_ADDR to ensure that new vault commands point at the local instance of Vault, replacing example.com with your domain.

        export VAULT_ADDR=https://example.com:8200
        
      5. Set the VAULT_TOKEN environment variable to the new token just created by the token create command. Remember that your actual token will be different than the one in this example.

        export VAULT_TOKEN=s.YdpJWRRaEIgdOW4y72sSVygy
        
      6. Now attempt to read our secret in Vault at the kv/myservice path.

        vault kv get kv/myservice
        

        Vault should return the key/value data.

          
        ====== Metadata ======
        Key              Value
        ---              -----
        created_time     2019-03-31T04:35:38.631167678Z
        deletion_time    n/a
        destroyed        false
        version          1
        
        ====== Data ======
        Key          Value
        ---          -----
        api_token    secretvalue
        
        
      7. To illustrate forbidden operations, attempt to list all secrets in the KV backend.

        vault kv list kv/
        

        Vault should deny this request.

          
        Error listing kv/metadata: Error making API request.
        
        URL: GET https://example.com:8200/v1/kv/metadata?list=true
        Code: 403. Errors:
        
        * 1 error occurred:
                * permission denied
        
        
      8. In contrast, attempt to perform the same operation in the previous terminal window that has been configured with the root token.

        vault kv list kv/
        
          
        Keys
        ----
        myservice
        
        

        The root token should have sufficient rights to return a list of all secret keys under the kv/ path.

      Authentication Methods

      In practice, when services that require secret values are deployed, a token should not be distributed as part of the deployment or configuration management. Rather, services should authenticate themselves to Vault in order to acquire a token that has a limited lifetime. This ensures that credentials eventually expire and cannot be reused if they are ever leaked or disclosed.

      Vault supports many types of authentication methods. For example, the Kubernetes authentication method can retrieve a token for individual pods. As a simple illustrative example, the following steps will demonstrate how to use the AppRole method.

      The AppRole authentication method works by requiring that clients provide two pieces of information: the AppRole RoleID and SecretID. The recommendation approach to using this method is to store these two pieces of information in separate locations, as one alone is not sufficient to authenticate against Vault, but together, they permit a client to retrieve a valid Vault token. For example, in a production service, a RoleID might be present in a service’s configuration file, while the SecretID could be provided as an environment variable.

      1. Enable the AppRole authentication method using the auth subcommand. Remember to perform these steps in the terminal window with the root token stored in the VAULT_TOKEN environment variable, otherwise Vault commands will fail.

        vault auth enable approle
        
      2. Create a named role. This will define a role that can be used to “log in” to Vault and retrieve a token with a policy associated with it. The following command creates a named role named my-application which creates tokens valid for 10 minutes which will have the read-myservice policy associated with them.

        vault write auth/approle/role/my-application 
            token_ttl=10m 
            policies=read-myservice
        
      3. Retrieve the RoleID of the named role, which uniquely identifies the AppRole. Note this value for later use.

        vault read auth/approle/role/my-application/role-id
        
          
        Key        Value
        ---        -----
        role_id    147cd412-d1c2-4d2c-c57e-d660da0b1fa8
        
        

        In this example case, RoleID is 147cd412-d1c2-4d2c-c57e-d660da0b1fa8. Note that your value will be different.

      4. Finally, read the secret-id of the named role, and save this value for later use as well.

        vault write -f auth/approle/role/my-application/secret-id
        
          
        Key                   Value
        ---                   -----
        secret_id             2225c0c3-9b9f-9a9c-a0a5-10bf06df7b25
        secret_id_accessor    30cbef6a-8834-94fe-6cf3-cf2e4598dd6a
        
        

        In this example output, the SecretID is 2225c0c3-9b9f-9a9c-a0a5-10bf06df7b25.

      5. Use these values to generate a limited-use token by performing a write operation against the AppRole API. Replace the RoleID and SecretID values here with your own.

        vault write auth/approle/login 
            role_id=147cd412-d1c2-4d2c-c57e-d660da0b1fa8 
            secret_id=2225c0c3-9b9f-9a9c-a0a5-10bf06df7b25
        

        The resulting output should include a new token, which in this example case is s.coRl4UR6YL1sqw1jXhJbuZfq

          
        Key                     Value
        ---                     -----
        token                   s.3uu4vwFO8D1mG5S76IG04mck
        token_accessor          fi3aW4W9kZNB3FAC20HRXeoT
        token_duration          10m
        token_renewable         true
        token_policies          ["default" "read-myservice"]
        identity_policies       []
        policies                ["default" "read-myservice"]
        token_meta_role_name    my-application
        
        
      6. Open one more terminal tab or window and log in to your remote host running Vault.

      7. Once again, set the VAULT_ADDR environment variable to the correct value to communicate with your local Vault instance.

        export VAULT_ADDR=https://example.com:8200
        
      8. Set the VAULT_TOKEN environment variable to this newly created token. From the previous example output, this would be the following (note that your token will be different).

        export VAULT_TOKEN=s.3uu4vwFO8D1mG5S76IG04mck
        
      9. Read the KV path that this token should be able to access.

        vault kv get kv/myservice
        

        The example should should be read and accessible.

      10. If you read this value using this Vault token after more than 10 minutes have elapsed, the token will have expired and any read operations using the token should be denied. Performing another vault write auth/approle/login operation (detailed in step 5) can generate new tokens to use.

      More Information

      You may wish to consult the following resources for additional information on this topic. While these are provided in the hope that they will be useful, please note that we cannot vouch for the accuracy or timeliness of externally hosted materials.

      Find answers, ask questions, and help others.

      This guide is published under a CC BY-ND 4.0 license.



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      Introduction to HashiCorp Configuration Language (HCL)


      Updated by Linode Written by Linode

      HCL is a configuration language authored by HashiCorp. HCL is used with HashiCorp’s cloud infrastructure automation tools, like Terraform. The language was created with the goal of being both human and machine friendly. It is JSON compatible, which means it is interoperable with other systems outside of the Terraform product line.

      This guide provides an introduction to HCL syntax and some commonly used HCL terminology.

      HCL Syntax Overview

      HashiCorp’s configuration syntax is easy to read and write. It was created to have a more clearly visible and defined structure when compared with other well known configuration languages, like YAML.

      ~/terraform/main.tf
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      # Linode provider block. Installs Linode plugin.
      provider "linode" {
          token = "${var.token}"
      }
      
      variable "region" {
        description = "This is the location where the Linode instance is deployed."
      }
      
      /* A multi
         line comment. */
      resource "linode_instance" "example_linode" {
          image = "linode/ubuntu18.04"
          label = "example-linode"
          region = "${var.region}"
          type = "g6-standard-1"
          authorized_keys = [ "my-key" ]
          root_pass = "example-password"
      }
          

      Note

      Key Elements of HCL

      • HCL syntax is composed of stanzas or blocks that define a variety of configurations available to Terraform. Provider plugins expand on the available base Terraform configurations.

      • Stanzas or blocks are comprised of key = value pairs. Terraform accepts values of type string, number, boolean, map, and list.

      • Single line comments start with #, while multi-line comments use an opening /* and a closing */.

      • Interpolation syntax can be used to reference values stored outside of a configuration block, like in an input variable, or from a Terraform module’s output.

        An interpolated variable reference is constructed with the "${var.region}" syntax. This example references a variable named region, which is prefixed by var.. The opening ${ and closing } indicate the start of interpolation syntax.

      • You can include multi-line strings by using an opening <<EOF, followed by a closing EOF on its own line.

      • Strings are wrapped in double quotes.

      • Lists of primitive types (string, number, and boolean) are wrapped in square brackets: ["Andy", "Leslie", "Nate", "Angel", "Chris"].

      • Maps use curly braces {} and colons :, as follows: { "password" : "my_password", "db_name" : "wordpress" }.

      See Terraform’s Configuration Syntax documentation for more details.

      Providers

      In Terraform, a provider is used to interact with an Infrastructure as a Service (IaaS) or Platform as a Service (PaaS) API, like the Linode APIv4. The provider determines which resources are exposed and available to create, read, update, and delete. A credentials set or token is usually required to interface with your service account. For example, the Linode Terraform provider requires your Linode API access token. A list of all official Terraform providers is available from HashiCorp.

      Configuring a Linode as your provider requires that you include a block which specifies Linode as the provider and sets your Linode API token in one of your .tf files:

      ~/terraform/terraform.tf
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      provider "linode" {
          token = "my-token"
      }

      Once your provider is declared, you can begin configuring resources available from the provider.

      Note

      Providers are packaged as plugins for Terraform. Whenever declaring a new provider in your Terraform configuration files, the terraform init command should be run. This command will complete several initialization steps that are necessary before you can apply your Terraform configuration, including downloading the plugins for any providers you’ve specified.

      Resources

      A Terraform resource is any component of your infrastructure that can be managed by your provider. Resources available with the Linode provider range from a Linode instance, to a block storage volume, to a DNS record. Terraform’s Linode Provider documentation contains a full listing of all supported resources.

      Resources are declared with a resource block in a .tf configuration file. This example block deploys a 2GB Linode instance located in the US East data center from an Ubuntu 18.04 image. Values are also provided for the Linode’s label, public SSH key, and root password:

      ~/terraform/main.tf
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      resource "linode_instance" "WordPress" {
          image = "linode/ubuntu18.04"
          label = "WPServer"
          region = "us-east"
          type = "g6-standard-1"
          authorized_keys = [ "example-key" ]
          root_pass = "example-root-pass"
      }

      HCL-specific meta-parameters are available to all resources and are independent of the provider you use. Meta-parameters allow you to do things like customize the lifecycle behavior of the resource, define the number of resources to create, or protect certain resources from being destroyed. See Terraform’s Resource Configuration documentation for more information on meta-parameters.

      Modules

      A module is an encapsulated set of Terraform configurations used to organize the creation of resources in reusable configurations.

      The Terraform Module Registry is a repository of community modules that can help you get started creating resources for various providers. You can also create your own modules to better organize your Terraform configurations and make them available for reuse. Once you have created your modules, you can distribute them via a remote version control repository, like GitHub.

      Using Modules

      A module block instructs Terraform to create an instance of a module. This block instantiates any resources defined within that module.

      The only universally required configuration for all module blocks is the source parameter which indicates the location of the module’s source code. All other required configurations will vary from module to module. If you are using a local module you can use a relative path as the source value. The source path for a Terraform Module Registry module will be available on the module’s registry page.

      This example creates an instance of a module named linode-module-example and provides a relative path as the location of the module’s source code:

      ~/terraform/main.tf
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      module "linode-module-example" {
          source = "/modules/linode-module-example"
      }

      Authoring modules involves defining resource requirements and parameterizing configurations using input variables, variable files, and outputs. To learn how to write your own Terraform modules, see Create a Terraform Module.

      Input Variables

      You can define input variables to serve as Terraform configuration parameters. By convention, input variables are normally defined within a file named variables.tf. Terraform will load all files ending in .tf, so you can also define variables in files with other names.

      • Terraform accepts variables of type string, number, boolean, map, and list. If a variable type is not explicitly defined, Terraform will default to type = "string".

      • It is good practice to provide a meaningful description for all your input variables.

      • If a variable does not contain a default value, or if you would like to override a variable’s default value, you must provide a value as an environment variable or within a variable values file.

      Variable Declaration Example

      ~/terraform/variables.tf
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      variable "token" {
        description = "This is your Linode APIv4 Token."
      }
      
      variable "region" {
          description: "This is the location where the Linode instance is deployed."
          default = "us-east"
      }

      Two input variables named token and region are defined, respectively. The region variable defines a default value. Both variables will default to type = "string", since a type is not explicitly declared.

      Supplying Variable Values

      Variable values can be specified in .tfvars files. These files use the same syntax as Terraform configuration files:

      ~/terraform/terraform.tfvars
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      token = "my-token"
      region = "us-west"

      Terraform will automatically load values from filenames which match terraform.tfvars or *.auto.tfvars. If you store values in a file with another name, you need to specify that file with the -var-file option when running terraform apply. The -var-file option can be invoked multiple times:

      terraform apply 
      -var-file="variable-values-1.tfvars" 
      -var-file="variable-values-2.tfvars"
      

      Values can also be specified in environment variables when running terraform apply. The name of the variable should be prefixed with TF_VAR_:

      TF_VAR_token=my-token-value TF_VAR_region=us-west terraform apply
      

      Note

      Environment variables can only assign values to variables of type = "string"

      Referencing Variables

      You can call existing input variables within your configuration file using Terraform’s interpolation syntax. Observe the value of the region parameter:

      ~/terraform/main.tf
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      resource "linode_instance" "WordPress" {
          image = "linode/ubuntu18.04"
          label = "WPServer"
          region = "${var.region}"
          type = "g6-standard-1"
          authorized_keys = [ "example-key" ]
          root_pass = "example-root-pass"
      }

      Note

      If a variable value is not provided in any of the ways discussed above, and the variable is called in a resource configuration, Terraform will prompt you for the value when you run terraform apply.

      For more information on variables, see Terraform’s Input Variables documentation.

      Interpolation

      HCL supports the interpolation of values. Interpolations are wrapped in an opening ${ and a closing }. Input variable names are prefixed with var.:

      ~/terraform/terraform.tf
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      provider "linode" {
          token = "${var.token}"
      }

      Interpolation syntax is powerful and includes the ability to reference attributes of other resources, call built-in functions, and use conditionals and templates.

      This resource’s configuration uses a conditional to provide a value for the tags parameter:

      ~/terraform/terraform.tf
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      resource "linode_instance" "web" {
          tags = ["${var.env == "production" ? var.prod_subnet : var.dev_subnet}"]
      }

      If the env variable has the value production, then the prod_subnet variable is used. If not, then the variable dev_subent is used.

      Functions

      Terraform has built-in computational functions that perform a variety of operations, including reading files, concatenating lists, encrypting or creating a checksum of an object, and searching and replacing.

      ~/terraform/terraform.tf
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      resource "linode_sshkey" "main_key" {
          label = "foo"
          ssh_key = "${chomp(file("~/.ssh/id_rsa.pub"))}"
      }

      In this example, ssh_key = "${chomp(file("~/.ssh/id_rsa.pub"))}" uses Terraform’s built-in function file() to provide a local file path to the public SSH key’s location. The chomp() function removes trailing new lines from the SSH key. Observe that the nested functions are wrapped in opening ${ and closing } to indicate that the value should be interpolated.

      Note

      Running terraform console creates an environment where you can test interpolation functions. For example:

      terraform console
      
        
      > list("newark", "atlanta", "dallas")
      [
        "newark",
        "atlanta",
        "dallas",
      ]
      >
      
      

      Terraform’s official documentation includes a complete list of supported built-in functions.

      Templates

      Templates can be used to store large strings of data. The template provider exposes the data sources for other Terraform resources or outputs to consume. The data source can be a file or an inline template.

      The data source can use Terraform’s standard interpolation syntax for variables. The template is then rendered with variable values that you supply in the data block.

      This example template resource substitutes in the value from ${linode_instance.web.ip_address} anywhere ${web_ip} appears inside the template file ips.json:

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      data "template_file" "web" {
          template = "${file("${path.module}/ips.json")}"
      
          vars {
              web_ip = "${linode_instance.web.ip_address}"
          }
      }

      You could then define an output variable to view the rendered template when you later run terraform apply:

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      output "ip" {
        value = "${data.template_file.web.rendered}"
      }

      Terraform’s official documentation has a list of all available components of interpolation syntax.

      Next Steps

      Now that you are familiar with HCL, you can begin creating your own Linode instance with Terraform by following the Use Terraform to Provision Linode Environments guide.

      More Information

      You may wish to consult the following resources for additional information on this topic. While these are provided in the hope that they will be useful, please note that we cannot vouch for the accuracy or timeliness of externally hosted materials.

      Find answers, ask questions, and help others.

      This guide is published under a CC BY-ND 4.0 license.



      Source link