Add ability to run Atlantis as a deployment

[jacob-jameson]

what

My team and I have added the ability to deploy Atlantis using a deployment controller rather than a statefulSet. This also included adding the ability to create a seperate PVC for atlantis-data, which may help with PR 304 - Move atlantis-data volume to a separate PVC.

The type of controller used to deploy Atlantis is determined by a new setting .Values.atlantisController which has a default value of statefulSet. In the absence of this setting, a statefulSet controller will be created by default. This means that the changes are completely backwards compatible with the current default values.yaml file.

The deployment is configured through the values.yaml file in the .Values.deployment object.

In the event that the Atlantis cluster is scaled to zero and quickly scaled to one again, to prevent two pods from simultaneously trying to access the same lock and plan files we use .Values.deployment.strategy: "Recreate" by default.

why

We use KEDA to scale our Kubernetes clusters based on events, but we would like the ability to scale our Atlantis clusters based on HTTPS events. To do this we need to use the KEDA http-add-on, which currently only supports deployment type controllers.

tests

Deployment

We tested these changes by deploying Atlantis with deployment and statefulSet controllers using the modified Helm chart in this request. Both are able to successfully deploy and pass the UI test suggested in the README by running

helm test my-atlantis

Scaling

When running Atlantis with a deployment controller, one of the main concerns is data in the PVC surviving pod failure. To confirm that data in the atlantis-data directory in the PVC does survive pod failure we;

1. Launched an interactive terminal in the Atlantis Pod
2. Created a text file in the atlantis-data directory
3. Exited the interactive terminal
4. Scale down the cluster to zero and Immediately scale back up to 1
5. Launched an interactive terminal in the new Atlantis Pod
6. Checked that the text file was still present in theatlantis-data directory

Backwards Compatibility

We also used the following command to test the Manifests produced.

helm install atlantis-release atlantis/ --values atlantis/values.yaml --dry-run --debug | tee manifests.txt

I ran this command in three scenarios:

1. Old Helm Chart, with old default values file
2. New Helm Chart, with old default values file
3. New Helm Chart. with new default values file (with default statefulSet controller)

In all of these scenarios the manifests produced were exactly the same. (Tested by comparing stringified YAML output)

references

No references.

[jamengual]

thanks for the contribution @jacob-jameson , we will review shortly

[jacob-jameson]

The lint test failed because I forgot to bump the chart version number. What should I bump the version number to? Does this count as a Major/Minor/Patch update?

[jamengual]

since is not a breaking change let's update the minor version.

[jacob-jameson]

Ignore the previous commit. There is a mistake in the Maintainers section of the Chart

[jacob-jameson]

Could a Maintainer approve the Test Workflows please?

[GenPage]

LGTM, just need to dance around other pending approved PRs and bumping chart version

[jacob-jameson]

Is there anything I need to do pre-merge?

[jseiser]

@jacob-jameson

You need to set the chart version to 4.15.2 to it will pass the lint/test charts step.

[jacob-jameson]

Is it acceptable to give a reviewer write permissions on my branch so that they can update the chart version when they review my code? I can't keep up with the chart version changes, and I have no idea when the linting pipelines will be run, so they always fail.

[jamengual]

no, you should wait until is reviewed and approved and then bump the chart version

[jacob-jameson]

I think all linting tests should pass now. Could I please get a code review?

[jacob-jameson]

Can I get a review please?

[cc-robertson]

we also have the same requirement. LGTM, can we get a review?

[jamengual]

@jacob-jameson could you fix the conflict? Thanks.

[jacob-jameson]

Conflicts have been resolved. Awaiting Review

[jamengual]

@jacob-jameson please update the chart version

[jamengual]

@jacob-jameson I bumped the version for you but now we have a JSON schema validation so please update the values there.

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