Add automatic retry to fluent RestTemplate calls

[achudzik]

Hystrix doesn't handle automatic retry by design (see this tweet). Maybe Spring Retry can be used instead? All suggestions are welcomed.

[marcingrzejszczak]

Looks great! We may add a new retry method to the fluent api that could delegate to RetryOperations. We would have to check if aspects would new to be changed accordingly to place correlation ids.

[szpak]

Btw, I have never used Spring Retry in my project, but AFAIK the waiting process in SR is blocking (see ThreadWaitSleeper which seems to be used in different BackOffPolicy implementations). That would mean that given thread is blocked for long seconds or minutes which does not scale well.
Maybe there is a way to make it non blocking in Spring Retry (or you don't treat it as a problem), but there is a nice looking async-retry library written by @nurkiewicz which seems to address that issue.
The problem could be that async-retry officially only supports Java 8 while micro-infra-spring seems to be compatible also with 1.7.

[nurkiewicz]

the waiting process in SR is blocking (see ThreadWaitSleeper which seems to be used in different BackOffPolicy implementations)

That's right, at the time I wrote async-retry RetryTemplate couldn't be tweaked to use asynchronous retrying. That was the reason to start the project in the first place.

Maybe there is a way to make it non blocking in Spring Retry

Nope. See above.

library [...] which seems to address that issue

It depends on whether this is an issue for you or not. If your fluent RestTemplate is blocking by design, I see no problem here. But if it returns Future/CompletableFuture/rx.Observable (it should!), then wasting thread for mostly sleeping is a poor idea. In that case async-retry can be seamlessly integrated.

async-retry officially only supports Java 8

Yes, I was maintaining java7 branch for quite a while (using ListenableFuture from Guava rather then new CompletableFuture in JDK8) and it's only few commits behind master requiring Java 8. I simply didn't have time to support boring Java 7 branch ;-).

[marcingrzejszczak]

@nurkiewicz so maybe we could count on you on making this branch up to date? :) and maybe also a PR for this one? :D

[nurkiewicz]

Sorry, missed last comment. It should be fairly straightforward, Java 7 branch lacks one bug fix and is not in Maven Central. Please track progress in nurkiewicz/async-retry#4.

[nurkiewicz]

async-retry was just backported to Java 7. If I manage to find some time, I can look at this issue, but probably next in this week. Leave a comment if you start working on this ticket first.

Just keep in mind that Hystrix 1.4 RC1 brings very useful HystrixObservableCommand (Netflix/Hystrix#209) that would most likely fit quite well with asynchronous retrying. Give me some time to investigate it.

[marcingrzejszczak]

Ok let's do as you say - if any of us wants to pick it we will send a msg here about it. Otherwise it's yours. If you need any support just ping any of us.

[gotpist1]

@nurkiewicz Is it possible to use AsyncRetry with Springs AsyncRestTemplate? I messed around abit with it yesterday, but didn't get it to work. Stumbled upon this thread and thought i would ask the expert :)