Modified Redis Health Check

[Better-Boy]

Line - https://github.com/meedan/alegre/blob/develop/app/main/controller/healthcheck_controller.py#L44

# FIXME Redis database is not being tested by info()

Why the change from info() to ping() is necessary?

1. The purpose of healthcheck is to check if the redis cluster/server is up and running. You don't need any other info than True/Exception.
2. By default, redis has 16 databases, which can be addressed by their indexes starting from 0 and ending at 15. If any value other than None(defaults to 0) and 0 to 15 are given, ping() will raise a ResponseError: DB Index is out of range which is handled in the except block
3. The return value of ping() is True if the connection is fine with checking database details. No need to assign True explicitly

[Better-Boy]

@huslage @caiosba Can any of you guys review this PR?

[caiosba]

@huslage will this change work for the health checker?

[Better-Boy]

@caiosba @huslage Any Update on this PR?

[caiosba]

@huslage @dmou @sonoransun any of you know if that change is valid for the AWS healthchecker?

[sonoransun]

Looking at the change, using r.ping() instead of r.info() seems perfectly appropriate. There is additional information in info(), however, it doesn't look like any of that is necessary - only a server liveness check.

Regarding AWS, the Redis ElasticCache service for both QA and Live, qa-redis and live-redis respectively, are monitored via AWS, so there is no concern regarding ping() vs. info() in the context of AWS service health.

EDIT: one other note - if testing the database is desired (e.g. to check for data in it, rather than just that the service is alive) then it might be useful to use the dbsize command to check for records, if a healthy service should always have greater than zero entries.

[Better-Boy]

@sonoransun Thank you for reviewing the PR.

@caiosba Now that the PR is reviewed, can it be approved and merged?