Fetaure request: a way for consul-template to exit upon a failed key lookup

[eikenb]

Requested feature is pretty straightforward and is simply that they want consul-template to exit with an error if a key it is looking up in Consul does not exist.

It should work with the template_error_fatal setting.

Look into making this cover all backends but only if simple. Otherwise keep this consul specific.

[eikenb]

Poked around this today trying to figure out the best solution. My current idea is to add a simple error template function that returns an error in a place that. Having a function that returns an error means you can use it with the keyExists function to dynamically check and trigger an error in the template. Eg.

{{ if not (keyExists "foo") }}
    {{ error "key foo doesn't exist" }}
{{end}}

[eikenb]

Oh.. and using the above with the template_error_fatal setting will achieve the goal of this enhancement request.

[eikenb]

That was naive. Templates always render once through with everything failing to look up. So any sort of exists check will always fail the first time triggering the error.

[eikenb]

Added it as a top level option that triggers the error on any data lookup that fails 2 fetch attempts. The error happens on the second attempt as the first attempt is a special case that does some setup.

Note that setting this disables retries for failed lookup attempt errors.

[akamensky]

Does not seem to work.

Template:

$ cat some.tpl 
{{ key "/does/not/exist" }}

Executing as:

$ consul-template -template-error-fatal -once -template "some.tpl:out.txt"

Hangs indefinitely. And I keep seeing in Consul logs:

2023-01-30T17:36:57.248+1100 [DEBUG] agent.http: Request finished: method=GET url="/v1/kv/does/not/exist?index=50&stale=&wait=60000ms" from=127.0.0.1:45502 latency=1m2.449311662s

Unless you mean that I should be checking if key exists from inside template? Then this feature makes very little sense to me.

[jlouros]

I can also confirm using consul-template -template-error-fatal -once -template="some.tpl:out.txt" does not work.

Also tried passing a bool consul-template -template-error-fatal=true -once -template="some.tpl:out.txt" (multiple variations like: true, True, TRUE, 1) and nothing happens. Consul-template still waits for the key to be present.