feat(metric-architecture)!: remove loggregator support and make log-cache the default metric source

[geigerj0]

Some context upfront

Application Autoscaler comes with two different deployment variants:

1. Retrieving metrics from the Loggregator metric stack (legacy): This variant was initially introduced because Log Cache wasn't available at that time. It requires the metricsserver and metricssgateway jobs to be deployed via the deployment manifest.
2. Retrieving metrics from the Log Cache metric stack (new): This is the successor of the Loggregator variant that got introduced with Log cache client #659. This variant works without the metricsserver and metricssgateway jobs but requires the feature flag use_log_cache and to be configured and valid Log Cache properties to be set under the metricscollector property of the eventgenerator job.

What is this breaking change about?

This PR introduces a breaking change by removing the possibility to deploy Application Autoscaler with metrics retrieved from the Loggregator metric stack. In case you deploy Application Autoscaler with metricsserver- and metricsgateway-job, your deployment will fail.

Why is this breaking change necessary?

• There is no need to support two metric retrieval variants (Loggregator and Log Cache).
• Removing the Loggregator variant allows us to eliminate a significant amount of code and complexity (e.g., metricsserver and metricsgateway).

Migration FAQs

How can I switch from Loggregator to Log Cache?

1. Remove the configuration of the metricsserver and metricsgateway jobs from your deployment manifest.
2. Configure metricscollector of the eventgenerator job with valid Log Cache properties. Example:

   metricscollector:
     ca_cert: ((/bosh-autoscaler/cf/log_cache.ca))
     client_cert: ((/bosh-autoscaler/cf/log_cache.certificate))
     client_key: ((/bosh-autoscaler/cf/log_cache.private_key))
     port: 8080
     host: logcache

Do I need to take action if I am already using the feature flag use_log_cache?

If you are already using the Log Cache variant and have configured the use_log_cache feature flag in your deployment manifest, everything will continue to work. However, note that this feature flag has been removed, so configuring use_log_cache no longer has any effect. Feel free to remove use_log_cache from your deployment manifest .

[bonzofenix]

initial review, I still have more code to review. I will finish tomorrow morning

[bonzofenix]

lgtm

[sonarqubecloud]

Quality Gate failed

Failed conditions
40.5% Duplication on New Code (required ≤ 3%)

See analysis details on SonarCloud