zoonage/concourse-github-lambda

concourse-github-lambda

Lambda function for handling Github access tokens and deploy keys used by Concourse teams. See the terraform subdirectory for an example that should work (with minimal effort).

Why?

Our CI/CD (in our case Concourse) needs deploy keys to fetch code from Github, and access tokens to set statuses on commits or comment on pull requests. Instead of having teams do this manually, we can use this Lambda and simply pass a list of repositories that the team requires access to, and deploy keys will be generated and written to Secrets Manager (where it is available to their pipelines).

How?

This Lambda function is deployed to the same account as our Concourse.
It is given an integration ID and private key for two separate Github Apps.
A team adds a CloudWatch event rule with the configuration for which repositories they need access to, and under which organisation.
The lambda creates/rotates an access token and deploy key for each team, every 30min and 7 days respectively.

Usage

After you have checked out the prerequisites, either download a zip from the releases, or build it yourself by running make release in the root of this repository. After you have a binary, you can edit terraform/example.tf to your liking and deploy the example by running:

terraform init
terraform apply

NOTE: The aws/secretsmanager KMS Key Alias has to be created/exist before the lambda is deployed.

Team configuration

Example configuration for a Team (which is then passed as input in the CloudWatch event rule):

{
  "name": "example-team",
  "repositories": [
    {
      "name": "concourse-github-lambda",
      "owner": "telia-oss",
      "readOnly": "true"
    }
  ]
}

When the function is triggered with the above input, it will create a deploy key for telia-oss/concourse-github-lambda, write a private key to /concourse/example-team/concourse-github-lambda-deploy-key and access token to /concourse/example-team/telia-oss-access-token.

Prerequisites

Github Apps

This Lambda requires credentials for two separate Github Apps in order to generate deploy keys and access tokens. See the official documentation on Creating a Github App, and grant them the following permissions:

key-service (generates deploy keys): Repository administration (write)
token-service (generates access tokens): ... any permissions really, or no permissions if you prefer that.

E.g., to make use of all the features in github-pr-resource), you'll need the following permissions for the token-service:

Note that we went with two Github Apps because we did not want to generate access tokens from the key-service app, because the token would have admin access to all repositories where the app was installed, and unfortunately have not found a way to further scope down the privileges of the generated tokens. The compromise then is to have a 2nd github app (token-service) which has less dangerous permissions, which we can then use to generate the access tokens.

Secrets

This lambda uses aws-env to securely populate environment variables with their values from either AWS Secrets manager, SSM Parameter store or KMS. This makes it easy to handle credentials in a safe manner, and we recommend using secrets manager or SSM (over KMS) to pass the Github Apps credentials to the lambda function. Below is an example of setting up the required secrets for the example, using Secrets Manager:

aws secretsmanager create-secret \
  --name /concourse-github-lambda/token-service/integration-id \
  --secret-string "13024" \
  --region eu-west-1

aws secretsmanager create-secret \
  --name /concourse-github-lambda/token-service/private-key \
  --secret-string file:///Users/someone/Downloads/concourse-github-token-service.pem \
  --region eu-west-1

aws secretsmanager create-secret \
  --name /concourse-github-lambda/key-service/integration-id \
  --secret-string "13025" \
  --region eu-west-1

aws secretsmanager create-secret \
  --name /concourse-github-lambda/key-service/private-key \
  --secret-string file:///Users/someone/Downloads/concourse-github-key-service.pem \
  --region eu-west-1

To update the values, use update-secret and --secret-id instead of create-secret and --name. Otherwise the arguments can remain the same.

zoonage / concourse-github-lambda