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.
NoteThe 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
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.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.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).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
Follow the steps in our Secure HTTP Traffic with Certbot guide to acquire a TLS certificate.
Add a system group in order to grant limited read access to the TLS files created by Certbot.
sudo groupadd tls
Change the group ownership of certificate files in the Let’s Encrypt directory to
tls
.sudo chgrp -R tls /etc/letsencrypt/{archive,live}
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
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 indicateswget
is missing from your system, install thewget
package and try again.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
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
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 messagekeyserver receive failed: Syntax error in URI
, simply try rerunning thegpg
command again.Note
If you receive errors that indicate thedirmngr
software is missing or inaccessible, installdirmngr
using your package manager and run the GPG command again.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
Verify that the fingerprint output matches the fingerprint listed in the Secure Communications section of the HashiCorp Security page.
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
Extract the Vault executable to the local directory.
unzip vault_*_linux_amd64.zip
Note
If you receive an error that indicatesunzip
is missing from your system, install theunzip
package and try again.Move the
vault
executable into a system-wide location.sudo mv vault /usr/local/bin
Reset the ownership and permissions on the executable.
sudo chown root:root /usr/local/bin/vault sudo chmod 755 /usr/local/bin/vault
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
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
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
Add the
vault
user to the previously createdtls
group, which will grant the user the ability to read Let’s Encrypt certificates.sudo gpasswd -a vault tls
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
Create a systemd
service
file that will control how to runvault
persistently as a system daemon.- /etc/systemd/system/vault.service
-
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32
[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
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
-
1 2 3 4 5 6 7 8 9
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
Vault is now ready to run. Start the service using
systemctl
.sudo systemctl start vault
If desired, enable the service as well so that Vault starts at system boot time.
sudo systemctl enable vault
Confirm that Vault is operational by using the
vault
executable to check for the service’s status. Set theVAULT_ADDR
environment variable tohttps://example.com:8200
, replacingexample.com
with your own domain:export VAULT_ADDR=https://example.com:8200
vault
commands should now be sent to your local Vault instance. To confirm this, run thevault 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.
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.
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.
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.
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 theroot
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.
With
VAULT_ADDR
set appropriately, execute the unseal command.vault operator unseal
A prompt will appear:
Unseal Key (will be hidden):
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.
Perform the
unseal
command again.vault operator unseal
Enter a different unseal key when the prompt appears.
Unseal Key (will be hidden):
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.
Set the
VAULT_TOKEN
environment variable to the value of the previously-obtained root token. This token is the authentication mechanism that thevault
command will rely on for future interaction with Vault. The actual root token will be different in your environment.export VAULT_TOKEN=s.YijNa8lqSDeho1tJBtY02983
Use the
token lookup
subcommand to confirm that the token is valid and has the expected permissions.vault token lookup
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.
Enable the secret backend by using the
enable
Vault subcommand.vault secrets enable -version=2 kv
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
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
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.
Create the following Vault policy file.
- policy.hcl
-
1 2 3
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
.Load this policy into Vault using the
policy write
subcommand. The following command names the aforementioned policyread-myservice
.vault policy write read-myservice policy.hcl
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"]
Open another terminal window or tab and login to the same host that Vault is running on. Set the
VAULT_ADDR
to ensure that newvault
commands point at the local instance of Vault, replacingexample.com
with your domain.export VAULT_ADDR=https://example.com:8200
Set the
VAULT_TOKEN
environment variable to the new token just created by thetoken create
command. Remember that your actual token will be different than the one in this example.export VAULT_TOKEN=s.YdpJWRRaEIgdOW4y72sSVygy
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
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
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.
Enable the AppRole authentication method using the
auth
subcommand. Remember to perform these steps in the terminal window with the root token stored in theVAULT_TOKEN
environment variable, otherwise Vault commands will fail.vault auth enable approle
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 theread-myservice
policy associated with them.vault write auth/approle/role/my-application \ token_ttl=10m \ policies=read-myservice
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.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
.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
Open one more terminal tab or window and log in to your remote host running Vault.
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
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
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.
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.
- Vault Documentation Overview
- Vault Reference Architecture and Best Practices
- Vault Secrets Engines
- Vault Auth Methods
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