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Kind of confused, is this setup for their production deployments only? Does instagram involve any staging environments that would catch a lot of their issues ahead of time, such as failed test builds, bad commits etc? Are their developers allowed to commit directly to master or do they go through a formal pull-request process that gets signed off by someone?

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As mentioned in the article itself, Instagram uses code review (using Phabricator), and also uses automated continuous integration for running tests on each "diff", before it allows the change to be landed to master.

Depends what automated tests you run. You could catch things that are technically wrong, but what about things like the button being in the wrong place.

That's nots going to spew errors.

This class of errors is sometimes fairly easy to catch with canaries.

If a button is obscured or inactive/non-functional for some reason, then chances are some metric is going to be statistically varied enough to call out while in the canary phase.

For more manual canaries, this same approach can be used for metrics like memory usage, latency, number of upstream/database connections, and so forth. Of course, that could be the _purpose_ of the change, which is why it likely will be checked with manual canaries (ie, not the canaries used for the continuous deployment process).

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