fix(aws-elasticache)!: correct major engine version cannot be set on serverless cache for memcached

[go-to-k]

Issue # (if applicable)

Closes #76 .

Reason for this change

Correct major engine version cannot be set on serverless cache for memcached.

Currently the same MajorVersion property is used for all the engine.

export enum MajorVersion {
  /**
   * Version 7
   */
  VER_7 = '7',

  /**
   * Version 8
   */
  VER_8 = '8',
}

new aws_elasticache.ServerlessCache(this, 'ServerlessCache', {
  engine: aws_elasitcache.Engine.VALKEY,
  majorEngineVersion: aws_elasticache.MajorVersion.Ver_8
  vpc,
});

https://github.com/open-constructs/aws-cdk-library/blob/v0.1.0/src/aws-elasticache/serverless-cache.ts#L69-L79

But the major version 1.6 can only be specified for memcached.

And 7 and 8 for valkey and 7 for redis only can be specified.

Supported versions: https://docs.aws.amazon.com/AmazonElastiCache/latest/dg/engine-versions.html

FYI: https://docs.aws.amazon.com/AmazonElastiCache/latest/dg/VersionManagement.html

ElastiCache serverless caches support ElastiCache version 7.2 for Valkey and above, ElastiCache version 1.6 for Memcached and above, and ElastiCache 7.0 for Redis OSS and above.

Description of changes

Two approaches can be applied for the issue:

1. Adding a new version (1.6 / VER_1_6) for memcached in the existing enum property

This approach is adding the new version VER_1_6 to the existing enum.

But additional validation process for correct combinations is required and the usability is not good because users can choose any of the options even though different engines have different possible versions.

export enum MajorVersion {
  /**
-   * Version 7
+   * Version 7 for Valkey and Redis only
   */
  VER_7 = '7',

  /**
-   * Version 8
+   * Version 8 for Valkey only
   */
  VER_8 = '8',
+
+  /**
+   * Version 1.6 for Memcached only
+   */
+  VER_1_6 = '1.6',
}

2. Adding a new property for each engine, including version

I decided to use this approach in this PR.

This approach removes the existing engine and majorEngineVersion properties and adds a new serverlessCacheEngine property using Enum-like classes.

    new ocf.aws_elasticache.ServerlessCache(this, 'Valkey8', {
      serverlessCacheEngine: ocf.aws_elasticache.ServerlessCacheEngine.valkey({
        engineVersion: ocf.aws_elasticache.ValkeyEngineVersion.VER_8,
      }),
      vpc,
    });

    new ocf.aws_elasticache.ServerlessCache(this, 'Memcached1_6', {
      serverlessCacheEngine: ocf.aws_elasticache.ServerlessCacheEngine.memcached({
        engineVersion: ocf.aws_elasticache.MemcachedEngineVersion.VER_1_6,
      }),
      vpc,
    });

This would be a breaking change since it would remove existing properties, but we are still on version 0 so it is doable. I think it is too early to adopt Approach 1 for backward compatibility concerns. Approach 1 is not a good approach and is inconvenient for users.

Also, those old properties are required properties now, so we CANNOT use the feature flag alternative.

Description of how you validated changes

Both unit tests and integ tests.

Checklist

• My code adheres to the CONTRIBUTING GUIDE
• My pull request adheres to the Pull Request Rule
  • Do not omit the aws- part in the scope of the PR title if the PR relates to a specific AWS service module.
  • e.g.) feat(aws-s3): description of the change

Breaking Change

BREAKING CHANGE: The existing properties engine and majorEngineVersion for ServerlessCache will be removed, users will have to use the new property serverlessCacheEngine.

---

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache-2.0 license

[go-to-k]

Created the props instead of directly using majorVersion as arguments for the EngineVersion in case properties such as fullVersion are added in the future.

[go-to-k]

Considering the possibility that properties such as fullVersion may be added only for partial engines in the future, I have prepared props for each engine: ValkeyEngineVersionProps, RedisEngineVersionProps and MemcachedEngineVersionProps.

[go-to-k]

The EngineVersion class (property) is wrapped in the EngineProps for factory methods of the ServerlessCacheEngine to allow for the possibility of additional elements other than the version in the future.