Support registering multiple health checks.

[giladwolff]

What problem are we solving?

Today, the RegisterEntityPayload offers the legacy registration interface that allowed registering a single Check. Consul supports registering multiple health checks starting in 2015 (commit 674be58e55f). For backward compatibility they maintain support for passing a single Check. Here is the relevant excerpt from agent/consul/catalog_endpoint.go:

// Move the old format single check into the slice, and fixup IDs.
if args.Check != nil {
        args.Checks = append(args.Checks, args.Check)
        args.Check = nil
}

How are we solving the problem?

Let's switch from offering a single 'Check' to running multiple 'Checks'. This breaks backwards compatibility and drops support to consuls servers from 10 years ago.

Checks

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[github-actions]

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[x0rw]

Hey.
In the official API docs, Check is not marked as deprecated or as legacy.
I think someone reading the docs will naturally use Check, so it's better to keep it and document that Checks is preferred instead.

[kushudai]

Hi @x0rw, we discussed this.
The official documentation states that
Multiple checks can be provided by replacing Check with Checks and sending an array of Check objects.
When we examined the server code for consul however, it accepts both as well and appends Check to Checks.

This behavior is confusing/surprising. We're opting to expose just one field instead, which can be empty to represent the original None state.

[giladwolff]

see documentation here. Code is [here] (https://github.com/hashicorp/consul/blob/1e4639402af0843b1fb3fa4b56c1bdd9eb2773d3/agent/consul/catalog_endpoint.go#L151)