Quick intro to helm – a package manager for Kubernetes

helm-logoI suddenly realized that I haven’t blogged about Kubernetes for quite a while. But there’s so much happening in that area! For instance, even though creating Kubernetes objects from YAML configuration was the true way, it never felt that much convenient. So here’s the solution – use helm, the package manager for Kubernetes.

What’s helm

Helm allows installation of Kubernetes apps in the same manner as we’d install TypeScript via npm or nginx via apt-get. It actually comes as two components: a command line client called helm and its companion service hosted inside of Kubernetes called tiller. Together they can search, install, remove, upgrade and create new application packages called charts.

‘Chart’ is not the only potentially confusing choice of words. For example, the instance of a chart running in Kubernetes is called a release. Two instances of the same chart would become two releases, and so forth.

Fortunately, the packages source has more conventional name – a repository. Obviously, there can be more than one of them, including privately maintained.

Having terminology sorted out, let’s install helm and see it in action.

Install

Well, it’s easy. Any of main OS package managers (brew, apt-get, chocolatey) can install helm. In my case brew install helm does the trick.

However, this only installs command line client. In order to make the whole thing to work we also need to install the server component – tiller – into Kubernetes cluster. I’ve started my cluster locally via minikube start and helm init will take care of the rest.

As a side note, it’s actually possible to see what exactly gets installed: helm init --output yaml spits out pretty trivial Deployment YAML that tiller is made of:

Basic operations

OK, it’s there, it’s working, let’s do something. For instance, let’s find some chart, install it, check its status and then remove it.

Search

First, let’s find something to install. helm search is the command to show all known packages. In fact, I already know what I want to try, so helm search prometheus narrows the search down to just a handful of packages:

Install

stable/prometheus seems to be the one I need, so without further ado:

It’s actually very convenient. Notes section in the end shows some info about what was installed and where to go next. For instance, there’re some suggested commands at lines 17-18 which will forward local port 9093 to exposed port of Alertmanager service, so we could point the browser to it and check what’s inside.

alertmanager

Btw, we could see the same notes again with the help of helm status %release name% command.

List installed charts

It’s also quite easy to see that prometheus indeed was installed:

Pay attention to REVISION column (the second one). That will come in handy once we get to upgrades and rollbacks.

Delete release

Well, that’s pretty obvious. helm delete %release name% will do the trick. I don’t really want to do that now, but adding --dry-run argument would help to see how it would go:

Advanced operations

Customizing installation

Installing preconfigured charts is not as useful as to be able to configure how exactly they are going to be installed.

See customizable options

While it’s possible to change virtually any parameter of the chart, it’s still a questions which ones do we have? helm inspect knows the answer:

Apply options

As you can see (actually you can’t, as I truncated the output, but believe me on this one), it has lots and lots of customizable values. If I wanted to disable the Alertmanager during installation, I’d probably put alertmanager.enabled=false to separate config file and passed it as an additional argument to install command:

Alternatively, it’s also possible to pass this value directly, without the file at all:

However, as we already installed prometheus, it would be way simpler to just upgrade it.

Upgrade and rollback

Upgrade

If we replace install with upgrade, we can pass new chart settings to existing release:

It looks like alertmanager didn’t appear in the output this time, but let’s check to be sure:

Nope, it’s gone.

Rollback

In case we changed our minds and want to revert back to previous version, there’s nothing easier. Simply pick the latest stable revision (remember that second column value in helm list, 1?) and call rollback:

We also can get back to list of revisions anytime with history command:

Easy peasy.

Create own chart

Of cause, we can and should create our own chart.

Create chart

There’s helper command helm create which creates a boilerplate template:

So Chart.yaml obviously is chart definition with the name and other stuff, whereas charts seems to be the folder for charts-dependencies. values.yaml is quite interesting. All those parameters we could see in helm inspect values and which we could change in helm install/upgrade are actually coming from here.

Templates

Checking the contents of templates folder reveals one important secret – all these deployments, services and other Kubernetes goodies that we’re going to ship in our package and which will be stored in templates folder – they all can be templates.

Here’s how it could be useful. For instance, if we don’t want to hardcode some Deployment’s name in YAML and rather pick one assigned to release with some suffix, here’s how we could do that:

.Release (as well as .Values) is one of helm’s built-in objects that templates can use. There’re few other sources of values, but simple value substitutions is not the only thing that templates are capable of. They also have control structures like if or range, some functions or even pipelines, so {{ .Release.Name | upper }} is perfectly valid template entry.

Packing and installing the chart

In fact, folder with the chart is already perfectly installable entity, so helm install ./demo-chart would actually work. However, if we’re going to distribute the chart or upload it to our own charts repository, it would make more sense to pack it first:

This creates a tarball, which, but the way, is also installable.

Conclusion

So this is helm. It’s actually pretty neat: easy to use, quite easy to understand and definitely more powerful than I need for foreseeable future. If only it could not exist and simply be a part of some already existing package manager. After all, how can I possibly keep remembering all of them? Even JavaScript has three. Can we have, maybe, just one to rule them all? Please?

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