feat(provider): choose between constant & exponential backoff for actions

[beagleknight]

This changes the poll backoff function to use ConstantBackoff instead of ExponentialBackoff. The current poll_interval option is a bit misleading because assumes a constant polling interval instead of an exponential one. This causes to wait much more time in some scenarios where you requested the resource status to the API a few times.

In scenarios where you expect a specific amount of time, such as creating a cloud instance with a custom snapshot, this change makes the behavior more predictable.

[jooola]

I agree that poll_interval suggests a constant backoff. But we need to be cautious with such change as it might introduce rate limits errors for some users.

The origin of this change is c8d8905

Maybe we want to provide an extra setting such as poll_function = oneOf('constant', 'exponential').

The same change must be made to the plugin provider:

terraform-provider-hcloud/hcloud/plugin_provider.go

Line 124 in 4811531

opts = append(opts, hcloud.WithPollBackoffFunc(hcloud.ExponentialBackoff(2, pollInterval)))

[apricote]

I agree with what @jooola said.

To explain the reasoning for switching it to exponential: The default rate limit for actions is 2 requests per second. If Terraform creates and waits for 5 resources (with refreshes every 500ms), you can get into a situation where the rate limit is exhausted and you can not really make progress, because every request you make is just using up the limit once again.

By using an exponential backoff you avoid this issue, because you just wait for longer between the API calls.

In scenarios where you expect a specific amount of time, such as creating a cloud instance with a custom snapshot, this change makes the behavior more predictable.

In my experience this time is highly variable, depending on the load on the snapshot storage. How long did you wait and how long did you expect it to take? Perhaps we need some kind of upper limit in the exponential backoff (maybe 30-60 seconds), to avoid situations like this.

Making constant vs. exponential configurable sounds good to me, I would prefer the exponential default though.

[fcsonline]

I have to say that I share the same thoughts as @beagleknight about the expected constant behaviour, but I also understand the risk of introducing a new behaviour combined with the 500ms that will cause much pain. The best solution, as you said is a new configuration option with the exponential default for backward compatibility.

[beagleknight]

Thanks for your replies @jooola and @apricote .
I just updated the code to allow users to configure the polling function. I'm not sure if the code is ok, since I don't have much knowledge about go. Can you please review it?

[apricote]

Thanks! I will take another look tomorrow :)

[apricote]

This is already looking pretty good :) I have updated the PR title to match the new content (as we use it for generating the Changelog).

There is one remaining inconsistency between the two providers. Do not worry about the failed integration tests, they do not work for external contributors. If you want, you can fix the formatting (see unit tests & lint job), otherwise, I can also take care of it before merging :)

EDIT: Docs are also missing, but I can also do them before merging if you dont want to.

[beagleknight]

Hey @apricote ! Thanks for your comments. I already addressed them and squashed all commits. Can you review it when you have some time? Thank you!

[apricote]

One more issue i found through the unit tests.

I tried to fix and push to the branch myself, but looks like this is disabled.

[apricote]

Tests are still failing because an import for "github.com/hashicorp/terraform-plugin-sdk/v2/helper/validation" is missing in hcloud/provider.go, could you add this and run make test locally to verify that it works?

[beagleknight]

@apricote Sorry for the late response! I just added the missing import to the code (and finally installed the devtools in vscode 😄 )

[apricote]

Thank you very much @beagleknight! Will be included in the next release :)

[beagleknight]

Hey @apricote ! Do you know when the next version will be released? We would like to use this change in our template :). Thanks!

[apricote]

Hey @apricote ! Do you know when the next version will be released? We would like to use this change in our template :). Thanks!

Released in v1.45.0

[fcsonline]

Thank you so much for the release, @apricote !! Testing it right now.