[APM] Don't read APM index names directly from config

[sorenlouv]

In #48079 APM added support for overriding index names defined in kibana.yml via the UI. This means that reading a config value directly from the config might give a stale result, since it's being overridden by the UI settings.

Instead of reading directly from the config file one should read both from the config file and the UI settings and merge the result. Fortunately this is already taken care of by getApmIndices.

Example: apm_oss.transactionIndices
Instead of getting apm_oss.transactionIndices via config.get('apm_oss.transactionIndices') one should instead get it like:

import { getApmIndices } from 'x-pack/legacy/plugins/apm/server/lib/settings/apm_indices/get_apm_indices'

const apmIndices = getApmIndices(server)
const transactionIndices = apmIndices['apm_oss.transactionIndices']

Fix in

• x-pack/legacy/plugins/infra/server/routes/metadata/lib/has_apm_data.ts
• src/legacy/core_plugins/kibana/server/tutorials/apm/envs/on_prem.js

[elasticmachine]

Pinging @elastic/apm-ui (Team:apm)

[elasticmachine]

Pinging @elastic/logs-metrics-ui (Team:logs-metrics-ui)

[jasonrhodes]

@elastic/apm-ui hey thanks for this heads up! I'm trying to use this in our NP shim layer now, where we will no longer have access to the server object. Can we talk through how we could make that possible?

[dgieselaar]

@jasonrhodes After #49455 lands, server will no longer be required, but as it stands, getApmIndices would still need the APM configuration object. Not sure what the right solution is, the infra plugin could make APM an optional dependency, or we could expose an API endpoint.

[jasonrhodes]

@dgieselaar I think the right solution will be for APM to return "getIndices" from its setup method, so that we can just call that directly. That is the place for plugins to share a contract, with types, as I understand it.