Docs: Add integration docs and some developer docs

Signed-off-by: John McBride <[email protected]>

Author: jpmcb

README.md

@@ -163,6 +163,20 @@ Note: We do not recommend using the Bottlerocket ECS Updater in conjunction with
 The ECS Updater is designed to keep services safe from interruption by updating one instance at a time.
 With the short average lifetime of Spot instances, the updater may not update them until relatively late in their life, meaning they may not be up to date when serving your application.
 
+## Developer guide
+
+To get started with building and developing the ECS updater, make sure you have:
+
+* [Go installed](https://go.dev/doc/install)
+* [`golangci-lint` installed locally](https://golangci-lint.run/usage/install/#local-installation)
+* make
+* [amazon-ecr-credential-helper](https://github.com/awslabs/amazon-ecr-credential-helper) setup for Docker and access to ECR (or your preferred image registry)
+* And the [cloud formation template linter installed](https://github.com/aws-cloudformation/cfn-lint)
+
+Make sure everything is ready and installed by running the tests with `make test`.
+Ensure the local builds work by running `make`.
+You might first need to get the modules downloaded to your local go mod cache by running `make tidy`.
+
 ## Security
 
 See [CONTRIBUTING](CONTRIBUTING.md#security-issue-notifications) for more information.

integ/README.md

@@ -0,0 +1,60 @@
+# Integration tests
+
+The following integration workflow is how you can
+test your changes and verifying that new dependencies didn’t break the updater mechanisms.
+It’s also similar to how we verify versions of the ECS Updater,
+so it’s useful to go through it when making changes
+and should in total take less than 1 hour.
+
+1. You’ll want to set up a test ECS cluster. 
+
+   Thankfully, this is really easy with the existing integration tests setup script:
+   https://github.com/bottlerocket-os/bottlerocket-ecs-updater/blob/develop/integ/setup.sh
+
+   ```sh
+   ./setup.sh --ami-id ami-05d2e4a6b8399095a
+   ```
+
+   This script expects the ami-id of a Bottlerocket ECS variant.
+   This will setup an ECS cluster using the integration CloudFormation stack
+   and using that Bottlerocket ECS variant as EC2 compute.
+
+2. Build an ECS updater image from your changes:
+
+   ```
+   # Build the image and tag it as "latest"
+   make image
+
+   # Verify the image was built and tagged a moment ago
+   docker images | head -n 10
+
+   # Re-tag the image to wherever you want to land it on your ECR registry
+   docker tag bottlerocket-ecs-updater:latest \
+       <account-id>.dkr.ecr.us-west-2.amazonaws.com/bottlerocket-ecs-updater:my-test
+
+   # Push it to your ECR registry
+   docker push \
+       <account-id>.dkr.ecr.us-west-2.amazonaws.com/bottlerocket-ecs-updater:my-test
+   ```
+
+3. Once your integration ECS cluster is up and you’ve built/pushed a new image,
+you can execute the run-updater script to actually do the integration tests!
+
+   Note that you need to provide the image URL of the new image you just built.
+   This is the actual image that gets deployed as a fargate task!
+
+   ```
+   ./run-updater.sh \
+       --cluster ecs-updater-integ-cluster \
+       --updater-image <account-id>.dkr.ecr.us-west-2.amazonaws.com/bottlerocket-ecs-updater:my-test
+   ```
+
+4. Cleanup is also easy! There’s a script for that as well: 
+
+   ```
+   ./cleanup.sh --cluster ecs-updater-integ-cluster
+   ```
+
+   This tears down the ECS cluster by name releasing any artifacts from the integration tests.
+
+In all, the total process takes well under an hour. ECS clusters spin up and down very quickly.