Human-friendly Duration serialization is not backwards-compatible

[jutley]

Recently, there have been changes to Duration to allow mixed units, e.g. 1h30m. When durations are serialized, they will include mixed units. This change will break older clients which do not know how to deserialize mixed unit durations. They will get an error that looks like not a valid duration string: "1h30m".

I think it would be a better implementation to serialize durations in a way that uses a single unit. This maintains backwards compatibility.

[brian-brazil]

Can you explain what this broke in Prometheus itself? I don't think we ever read back in these values, so this shouldn't be an issue.

[jutley]

I don't believe anything broke specifically within Prometheus. In our case, we use cortextool, which uses this library for parsing durations returned by a Prometheus/Cortex rules API. If Prometheus/Cortex is on a version with the new duration format and returns a mixed-unit duration, cortextool is unable to parse them.

At this point, cortextool has been updated, so it's not directly an issue for us anymore. I'm not sure how many other projects will have this issue, or whether compatibility for projects outside of the prometheus org is even a concern for this library.

Regardless, I think it's important to at least file this issue for discoverability in case someone else encounters this behavior.

[roidelapluie]

Thanks for your input. As it looks like there is no issue within Prometheus I'll close this. It does not seem the right repo for a placeholder issue like this, and cortex has released since.