a simple counter resource for concourse ci
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A Simple Counter Resource for Concourse

A simple incrementing counter to version concourse pipelines.

Overview

This is a simple resource that's meant to act as a simpler versioning scheme than the concourse provided semver.

The semver resource is great for a pipeline that publishes something for consumption (such as an executable or library).

However, there are a lot of cases in which a simple incrementing count would do. This resource is for pipelines that do not need the concept of a major, minor, or patch version.

If you currently use the semver resource but bump just one of major, minor, or patch, then this might be for you.

Resource Configuration

Currently s3 is the only backend that is supported for storing the state of the counter. As such, the source configuration for the counter resource deals with defining the s3 object that will store the counter.

Required fields:

  • bucket: The name of the s3 bucket
  • key: The name of the key within the bucket

Optional fields:

  • aws_access_key_id: The access key used for s3 access
  • aws_secret_access_key: The secret key used for s3 access
  • region: The region of the bucket

Note that boto3 is used internally. This means that any other way of providing credentials can be used (instance profiles, environment variables, or aws configure).

The following is an example resource configuration:

resources:
- name: counter
  type: counter-resource
  source:
    bucket: 'test-bucket'
    key: 'some_folder/counter/count'

resource_types:
- name: counter-resource
  type: docker-image
  source:
    repository: jinlee/counter-resource

Parameters

This section defines the parameters you can pass when using the resource in a task.

Get

There's only one optional parameter for the get task:

  • inc: Defaults to false. If set to true, will increment the counter locally, but not on s3

Note that concourse does seem to support the many ways of passing boolean values in yaml. Check the example.

Put

There's only one required parameter for the put task:

  • file: The path to the file with the count. In most cases this should be the same file placed with the get task. However, it can be any file with a single non-negative value.

Usage

The get task will place a file in resource-name/count, where the content is the count.

This resource should be the most useful when used in the first job of the pipeline. Its purpose is to tag a single run of the pipeline with a unique number. Use it with inc: true at the beginning of the job, and place the put task as the very last step. This ensures that you will only bump up the counter if the entire job was successful. Otherwise you would be bumping up the counter unnecessarily.

A simple get with an increment (with an example of how to use it with the s3 resource):

plan:
- get: counter
  params: {inc: yes}
- task:
  ... produce artifact-$(cat counter/count).jar ...
- put: s3
  params: {file: artifact-*.jar}
- put: counter
  params: {file: counter/count}

If the counter is required in a downstream job, leave out the inc:

plan:
- get: counter
  passed: [prev-job]
- task:
  ... do something ...

Check out the example pipeline using the counter resource.

Required S3 Policy

The resource requires just two s3 actions: s3:GetObject and s3:PutObject.

The IAM Policy should look something like this:

{
  "Version": "2012-10-17",
  "Statement": [
    {
      "Effect": "Allow",
      "Action": [ "s3:GetObject", "s3:PutObject" ],
      "Resource": [
        "arn:aws:s3:::test-bucket/some_folder/counter/count"
      ]
    }
  ]
}