Tuesday, May 28, 2013

Retrying things in ruby

Working with remote systems that are not always under your control often involves failures; I'm working on a system that does an API call on a remote system, and the remote system needs to call other systems to finish the call (it is calling a licensing server, from another company). The call already has timeouts and delays, but it crashes often enough, which requires me to restart the job (the job is inside a resque queue).

Now, if we try to do something, and it fails, it will usually raise an exception; Ruby has exception handling, including the rescue keyword, which will restart the block that started the exception; Ruby also has blocks, procs and lambdas, which allow us to pass a piece of code (OK, a closure :) to another function or method, so we can define a function as follows:

And then we could use it like:
Voila ! we now can easily retry our operation several times; if we wanted to be fancy, we could add a time to sleep between tries, and even define a small DSL for this, but for my needs this was enough.

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