Add Helm chart for MongoDB sharded cluster

[sejongk]

What this PR does / why we need it:
This PR adds a Helm chart for MongoDB, supporting both standalone mode and sharded cluster mode.
Shard rules, including shard keys, shard methods, and unique constraints, are defined and managed in the values.yaml.

This chart depends on the Bitnami's mongodb-sharded chart (https://github.com/bitnami/charts/tree/main/bitnami/mongodb-sharded).
There are a few known issues with it:

• A problem with livenessProbe and readinessProbe
  • Issues
    • [bitnami/mongodb] Inaccurate Checks in Bitnami Readiness and Startup Probes bitnami/charts#21957
  • Solution: use custom livenessProbe and readinessProbe instead
• Lack of ARM64 support in the Bitnami mongodb-sharded container
  • Issues
    • Support for ARM64 architecture in Bitnami container images bitnami/charts#7305 (comment)
    • [bitnami/mongodb] Mongodb doesn't run on M1 Mac bitnami/containers#40947
  • Solution: use the official mongo 6.0 image instead and set up the cluster via a Job.

How to install and uninstall

1. Create mongodb namespace

kubectl create namespace mongodb

2. Install helm chart with the set flag and the namespace flag (The reason why the namespace flag is needed to be set is due to the misguided value in the Bitnami chart. In here, it uses .Release.Namespace without offering an option to override it.

helm install mongodb . --namespace mongodb --set=sharded.enabled=true

3. Uninstall helm chart with the namespace flag

helm install mongodb . --namespace mongodb

Which issue(s) this PR fixes:

Addresses #673

Special notes for your reviewer:

We need to do following tasks in the future:

• Enable livenessProbe, readinessProbe
• Connect to Prometheus via PodMonitors

Does this PR introduce a user-facing change?:

Additional documentation:

Checklist:

• Added relevant tests or not required
• Didn't break anything

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (65712ec) 50.14% compared to head (6522060) 50.00%.
Report is 3 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #769      +/-   ##
==========================================
- Coverage   50.14%   50.00%   -0.15%     
==========================================
  Files          69       69              
  Lines       10182    10224      +42     
==========================================
+ Hits         5106     5112       +6     
- Misses       4534     4570      +36     
  Partials      542      542              

☔ View full report in Codecov by Sentry.
📢 Have feedback on the report? Share it here.

[hackerwins]

Thanks for your contribution.
I left a few comments.

[krapie]

Thank you for your contribution 😄
First off, I have left some small conventional suggestions along with comprehensive questions.

Question 1

It seems like yorkie-cluster Helm chart no longer has mongoDB subshart. This means that we now need to install both yorkie-cluster and yorkie-mongodb Helm chart to fully use yorkie cluster. Is there any reason for this separation?

Question 2

It seems like yorkie-mongodb Helm chart performs sharded mongoDB setup by using Job object. Is there any reason for this approach?

I can see that mongodb-sharded Helm chart provides common.initScriptsCM value to initialize mongoDB instances (Nevertheless I also think using Job is the best approach for this kind of operation, I just want to know the reasons for this approach).

Lack of ARM64 support in the Bitnami mongodb-sharded container
Solution: use the official mongo 6.0 image instead and set up the cluster via a Job.

Also, is there any relations between ARM64 support and setting up cluster via Job?

Suggestion 3

How about adding NOTES.txt to keep consistency with other yorkie Helm charts?

Suggestion 4

We might need to add ArgoCD Application manifest in yorkie-argocd Helm Chart as well.

[krapie]

LGTM 👍🏼

[hackerwins]

LGTM.

[sejongk]

Question 1

It seems like yorkie-cluster Helm chart no longer has mongoDB subshart. This means that we now need to install both yorkie-cluster and yorkie-mongodb Helm chart to fully use yorkie cluster. Is there any reason for this separation?

Question 2

It seems like yorkie-mongodb Helm chart performs sharded mongoDB setup by using Job object. Is there any reason for this approach?

I can see that mongodb-sharded Helm chart provides common.initScriptsCM value to initialize mongoDB instances (Nevertheless I also think using Job is the best approach for this kind of operation, I just want to know the reasons for this approach).

Lack of ARM64 support in the Bitnami mongodb-sharded container
Solution: use the official mongo 6.0 image instead and set up the cluster via a Job.

Also, is there any relations between ARM64 support and setting up cluster via Job?

Thanks for your careful review.
Here are my answers for your questions.

Answer 1

After separating MongoDB from yorkie-cluster, there are now two options for users: self-hosted or managed databases (e.g., MongoDB Atlas, AWS DynamoDB). I believe we can focus on supporting self-hosted clusters by solely maintaining yorkie-mongodb.

Answer 2

I initially explored the approach using Bitnami options and tools. Bitnami charts are designed to be used with Bitnami containers together. However, issues arose, including the lack of ARM64 images in the Bitnami mongodb-sharded container. Instead of incurring the current and potential future engineering costs associated with external tools, I opted to implement and maintain the code ourselves.
I believe the current requirements for this are relatively simple and manageable. If future requirements become more complex and there is a good alternative, that would be the time to consider such an option.