Buildkite Agent SSH keys

If your agent needs to clone your repositories using git and SSH, you'll need to configure your agent with a valid SSH key.

Finding your SSH key directory

When the Buildkite agent runs any git operations, it will look for SSH keys in ~/.ssh under the user the agent is running as. Each platform's agent installation documentation specifies which user the agent runs as and in which directory the SSH keys are. For example, on Debian the agent runs as buildkite-agent and the SSH keys are in /var/lib/buildkite-agent/.ssh/ but on macOS the agent runs as the user who started the launchd service, and the SSH keys are in that user's .ssh directory.

Debugging SSH key issues

To help debug SSH issues, you can enable verbose logging by running your build with the following environment variable set:

GIT_SSH_COMMAND="ssh -vvv"

Creating a single SSH key

The following shows an example of creating a new "machine user" SSH key for an agent:

$ sudo su buildkite-agent # or whichever user your agent runs as
$ mkdir -p ~/.ssh && cd ~/.ssh
$ ssh-keygen -t rsa -b 4096 -C "dev+build@myorg.com"
Generating public/private rsa key pair.
Enter file in which to save the key (/var/lib/buildkite-agent/.ssh/id_rsa):
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /var/lib/buildkite-agent/.ssh/id_rsa.
Your public key has been saved in /var/lib/buildkite-agent/.ssh/id_rsa.pub.
The key fingerprint is:
4b:6f:7b:5f:8e:f7:5b:c1:fa:e3:dd:9a:8e:a8:e8:33 dev@org.com
The key's randomart image is:
+---[RSA 4096]----+
|                 |
|                 |
|                 |
|              .  |
|        S      o |
|       . o    . .|
|        . o  .  o|
|      E. . o...*=|
|     .oo..o..oB*O|
+-----------------+
$ ls
id_rsa  id_rsa.pub
$ cat id_rsa.pub
ssh-rsa AAAAB3NzaC1yc2EAAAADAQABAAACAQDELESv1QGfoZ2hECJr.......Yho9hDPoNefDbcdZM4NdKWTVmyNGQo6YTzw== dev+build@myorg.com

You'd then add this key to the user's settings on GitHub, Bitbucket, GitLab, etc.

Creating multiple SSH keys

If you need to use multiple SSH keys for different pipelines, we support a special repository hostname format which you can use with your ~/.ssh/config.

To use a different key for a given pipeline, first change the repository hostname in your Buildkite pipeline settings from server.com to server.com-mypipeline, add an entry to the SSH config file on your agent machine for the host server.com-mypipeline, and specify your custom SSH key.

For example, if you had a pipeline repository URL of git@github.com:org/pipeline-1.git you would change it in your Buildkite repository settings to git@github.com-pipeline-1:org/pipeline-1.git and create the following SSH config file:

Host github.com-pipeline-1
  HostName github.com
  IdentityFile /var/lib/buildkite-agent/.ssh/id_rsa.pipeline-1

The following example shows how to create the corresponding pipeline-specific SSH key:

$ sudo su buildkite-agent # or whichever user your agent runs as
$ cd ~/.ssh
$ ssh-keygen -t rsa -b 4096 -C "dev+build-pipeline-1@myorg.com"
Generating public/private rsa key pair.
Enter file in which to save the key (/var/lib/buildkite-agent/.ssh/id_rsa): id_rsa.pipeline-1
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in id_rsa.pipeline-1.
Your public key has been saved in id_rsa.pipeline-1.pub.
The key fingerprint is:
e4:60:69:a3:a0:63:bb:27:e6:ff:53:d3:4a:06:7f:e4 dev@org.com
The key's randomart image is:
+---[RSA 4096]----+
|                 |
|       .         |
|  .   * .        |
| . . = = .       |
|o.  . o S        |
|...    * E       |
| .    + +        |
| o.. . .         |
|oo+....          |
+-----------------+
$ ls
id_rsa.pipeline-1  id_rsa.pipeline-1.pub

Alternatively, you can use a shorter approach to creating multiple SSH keys by adding pipeline-specific environments:

Note that if you are using Elastic CI Stack for AWS, the following approach is redundant as secrets support allows you to specify an SSH key per pipeline as /{pipeline-slug}/private_ssh_key.

Add a pipeline-specific environment (for example, by using Elastic CI Stack for AWS's secrets support or by having an Agent environment hook that switches on the repository URL or the pipeline slug):
```
GIT_SSH_COMMAND="ssh -i ~/.ssh/id_rsa_mypipeline"
```
Create an identity file at that location:
```
~/.ssh/id_rsa_mypipeline
```
Add the public key for that identity file to mypipeline on the git repository provider.

Using multiple keys with ssh-agent

If you need to use multiple keys, or want to use keys with pass-phrases, an alternative to the above hostname method is to use ssh-agent.

After starting an ssh-agent process and adding the keys, ensure the SSH_AUTH_SOCK environment variable is exported by your environment hook.

For example, if you set up ssh-agent like so:

$ sudo su buildkite-agent
$ ssh-agent -a ~/.ssh/ssh-agent.sock
$ export SSH_AUTH_SOCK=/var/lib/buildkite-agent/.ssh/ssh-agent.sock
$ ssh-add ~/.ssh/id_rsa-pipeline-1
Identity added: /var/lib/buildkite-agent/.ssh/id_rsa-pipeline-1
$ ssh-add ~/.ssh/id_rsa-pipeline-2
Identity added: /var/lib/buildkite-agent/.ssh/id_rsa-pipeline-2

The following environment hook will direct your build's git operations to use the ssh-agent socket:

#!/bin/bash

set -eu

export SSH_AUTH_SOCK="/var/lib/buildkite-agent/.ssh/ssh-agent.sock"