Improve server_preboot execution time

[afharo]

As a follow up to #108950 where we noticed that server_setup doubled its execution time in the past 30 days, affecting Kibana's total startup time, we now want to pay attention to any improvements we can apply to server_preboot to reduce the consistent 12s it takes to run:

After #108950, Kibana's total startup time is primarily affected by this step (approx 2/3s of the total time is taken by this step). If we manage to reduce it, it will be a huge win overall.

[elasticmachine]

Pinging @elastic/kibana-core (Team:Core)

[afharo]

After a quick research, I noticed this is the method where the preboot phase spends most of its time:

kibana/src/core/server/plugins/plugins_service.ts

Line 118 in 8f7e10a

await this.handleDiscoveredPlugins(plugin$);

It's going through all the plugins and generating their valid config with the provided schema. Each plugin takes, on average, 100ms in this process, and Kibana currently boots up with 100+ plugins, so it multiplies.

I think that the only possible action points here are to either:

• Improve the performance of our validation tool @kbn/config-schema is slow #78351
• Make this validation async somehow, so we can run multiple validations concurrently.

[mshustov]

After a quick research, I noticed this is the method where the preboot phase spends most of its time:

@afharo did you test it in dev mode? If so, IIRC Kibana spent most of the time compiling plugins code with @babel/register

[afharo]

@mshustov you are right! It's taking longer to run plugin.getConfigDescriptor() (that has a require() inside)

kibana/src/core/server/plugins/plugins_service.ts

Line 275 in 66dbb88

const configDescriptor = plugin.getConfigDescriptor();

than to run isEnabledAtpath (that internally validates the config)

kibana/src/core/server/plugins/plugins_service.ts

Line 292 in 66dbb88

const isEnabled = await this.coreContext.configService.isEnabledAtPath(plugin.configPath);

Well spotted.

[pgayvallet]

We did a lot of perf improvement on our whole startup time earlier this year, I think we can consider this one done.