Use one Helm chart for ALL microservices?

Question

This is a follow up question to my post Parameterized Kubernetes manifest files?.

I understand more about Helm now, after lots of reading, including the Learn Helm book (which I recommend). I still have this understanding that each microservice will have its OWN Helm chart? This defeats the purpose of what I wanted, where I just have ONE helm chart, and every time I want to use it, I just update the Chart.yml and values.yml files for each microservice, everything else is the same. For example, the microservice name, versions, and repo will change of course per microservice. Seems like I'm looking for a "template" for Chart.yaml and values.yaml. Is this possible to do? I don't know if it's recommended or not (I may not care).

I come from a CloudFoormation background, where I just have ONE parameterized CloudFormation template, and I just pass it parameters pertinent to each microservice.

UPDATE: I'm aware of Helm library charts, and I don't think they can provide the functionality I want?

Answer 1

Subcharts are the way to go.

I've done a very similar thing as follows:

• Create one or more base charts which cover microservices that have similar configuration (e.g. one for backend microservices, another for frontend servers).
• Create an overall chart for your application. This may be a bare bones chart without any resource configurations, but just a Chart.yaml and values.yaml. Or, you may also include some resources specific to your application overall and not a particular microservice (e.g. networkpolicy or ingress).

You could put everything in one git repo e.g.:

my-deployment-repo/
|- base-microservice/
   |- templates/
      |- deployment.yml
      |- service.yml
   |- Chart.yaml
   |- values.yaml
|- base-ui/
   |- templates/
      |- deployment.yml
      |- service.yml
   |- Chart.yaml
   |- values.yaml
|- myapp/
   |- Chart.yaml
   |- values.yaml

Then, your overall application chart (here myapp) can include the base charts multiple times as a dependency in its Chart.yaml. If you are putting all these charts in one git repo, you can use relative paths to point to them. E.g.

# Chart.yaml
dependencies:
  - alias: my-microservice-1
    name: base-microservice
    version: "0.1.0"
    repository: file://../base-microservice
  - alias: my-microservice-2
    name: base-microservice
    version: "0.1.0"
    repository: file://../base-microservice
  - alias: my-ui-1
    name: base-ui
    version: "0.1.0"
    repository: file://../base-ui
  - alias: my-ui-2
    name: base-ui
    version: "0.1.0"
    repository: file://../base-ui

The key thing here is alias. This allows charts to be depended on multiple times. It sets the name of the chart to the alias, so within the subcharts you can use {{.Chart.Name}}.

Finally, in myapp's values.yaml, you can pass different values to the subcharts under their alias key, e.g. if you have used {{.Values.image}} in base-microservice, you can do the following in myapp's values.yaml:

# values.yaml
my-microservice-1:
  image: foo
my-microservice-2:
  image: bar

When it comes to deploying myapp, run the following commands from within the myapp directory:

helm dependency update
helm install myapp .

You must always run helm dependency update before installing/upgrading a chart if any of the subcharts have changed.

I recommend git ignoring .tgz files, so you don't end up with .tgz files created by helm dependency update getting committed to your repo.

Answer 2

Generally, a Helm chart would cover all your microservices - ideally, you should be able to deploy whole application in one chart. It may get a little messy if you include external 3rd party dependencies, where you would need to handle dependent charts, but I assume this is out of scope of your question.

More so, if your microservices are very similar you could write for loops, such as:

{{- range $index, $service := .Values.myservices}}
apiVersion: apps/v1
kind: Deployment
metadata:
  name: myapp-{{ $service.name }}
# --- etc ---
{{- end }}

Now, where to put your chart - in most cases a preferred way is to have a separate repo for all Ops CD files, including Helm chart - so this is where Helm chart would live. This is not to be mixed with CI files, such as Dockerfile - those should live alongside microservice repositories themselves.

Answer 3

I believe what you're asking is: "Is there any way to create just one helm chart that can be used for all microservices in my application?". If so, then you can just use the values.yaml file to store all the values for your templates. This is not considered good practice, considering your template file needs to hold the information for each of your microservice deployments (and thus will become really difficult to manage), but it is possible.

One example: say you have two microservices, and you need one Helm chart that will create the template for both microservices. Generally, you would create separate templates for each service under the templates folder, and deploy each Helm chart for each service individually, but instead you could create multiple deployments in one template yaml file, like

# For service 1
apiVersion: apps/v1
type: Deployment
etc., etc... (stick in all values.yaml file values here for service 1)
---
# For service 2
apiVersion: apps/v1
type: Deployment
etc., etc... (stick in all values.yaml file values here for service 2)

In your values.yaml file, you would then just place in the values for each of your services, like

# Service 1 Keys/Values
foo: value
# Service 2 Keys/Values
bar: otherValue

So to answer your question, you can package all your services into one individual Helm chart using the above method, and Kubernetes will run each service as their own ReplicaSet as expected. However, when you have many services to manage, it can be tricky to manage the template YAML files and the values.yaml files when you put in values for all your services in one file, and so it's most likely not a good practice to do this.

This is just my understanding of Helm so far, as I'm still learning Helm myself. As such, I'm not 100% sure if this can be done, so you might want to double check with another person that this answer is actually correct.

EDIT: To summarize: like I mentioned above, in theory, it is possible to use one Helm chart per service. But in practice, it will be extremely messy later on to manage the values.yaml and the templates in the templates folder. So the answer would be, "Yes in theory, but not recommended at all".