Helmfile and friends

Having written a post on Helm, I feel obliged to follow it up with one on Helmfile, a project that addresses some of the issues that I identified with deploying multiple Helm charts. In particular, it provides an alternative approach to the umbrella chart mechanism that Jenkins X uses for deploying the set of charts that represent an environment.

Yet again, we have a go binary, available via brew install helmfile. At its most basic, we then have a helmfile.yaml that specifies a set of releases with a name, chart, namespace and override values for each. A helmfile sync will then perform an install/upgrade for all the releases defined in the file. One thing I failed to mention in my Helm post was that Helm supports plugins on the client side. One such plugin is the helm-diff plugin which, as you’d probably guess from the name, gives you a diff between the current state of a release and what it would look like after an upgrade or rollback. The plugin is installed with:

With this in place, we can now use helmfile diff to see the changes that would take place across all of our releases. The helmfile apply command combines this with a sync to conditionally perform an upgrade only if there are differences. There is a set of other helmfile commands that all perform aggregate operations across all the releases: delete, template, lint, status and test.

So far so good but nothing that couldn’t be achieved with a pretty short bash script. Where things get more interesting is that the helmfile.yaml is actually a template in the same way as the templates in a Helm chart. This means we can start to do more interesting things like defining values in one place and then reusing them across multiple releases. Helmfile has the explicit concept of an environment, passed in as a parameter on the CLI. We can use a single YAML file and use templating to have different values apply in each environment or, in the extreme, only deploy charts in some environments.

Helmfile also has some tricks up its sleeve when it comes to secrets. Most trivially, if your CI allows you to configure secrets via environment variables you can consume these directly in the helmfile.yaml. You can also store secrets in version control encrypted in a YAML file and then have another Helm plugin, helm-secrets, decrypt them with PGP or AWS KMS.

Helmfile has some features to help you as the size of your deployment grows. You can, for example, specify a selector on commands to only apply them to matching releases. This can be helpful if deploying all the changes at once is likely to create too much churn in your cluster. You can also split the file into multiple files in one directory (executed in lexical order) or over multiple directories (accessed via a glob syntax).

For anything else, there are prepare and cleanup hooks to allow you to execute arbitrary commands before and after deployment. Oh, and if you’re using a containerized deployment pipeline, it’s available packaged up in an image, ready for use. Finally, if you don’t take to Helmfile, take a look at Helmsman instead.

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