Aled Sage created JCLOUDS-1203:
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Summary: aws-ec2 rate-limiting causes provisioning to fail: need
longer back-off/retry
Key: JCLOUDS-1203
URL: https://issues.apache.org/jira/browse/JCLOUDS-1203
Project: jclouds
Issue Type: Bug
Affects Versions: 2.0.0, 1.9.2
Reporter: Aled Sage
TL;DR: increase default retry/back-off to 500ms and 6 retries.
In Apache Brooklyn (which uses jclouds), we hit {{Request limit exceeded}} when
provisioning VMs in aws-ec2 [1]. We were provisioning multiple machines
concurrently: different threads were independently calling
{{createNodesInGroup}}. The default exponential backoff and retry within
jclouds wasn't enough.
My understanding is that AWS will rate-limit based on the nature (as well as
number) of API calls. For example, if creating/modifying security groups is a
more expensive operation (from AWS's perspective) than a simple poll for a
machine's state, then those requests would cause rate-limiting sooner.
Within jclouds, the defaults are {{retryCountLimit = 5}} and {{delayStart =
50ms}} (see [2]).
This means we retry with the back-offs being (approximately) 50ms, 100ms,
200ms, 400ms and 500ms.
We overrode the defaults to be 500ms and 6 retries, and could then successfully
provision 20 VMs concurrently. Six of the 20 calls to {{RunInstances}} were
rate-limited. It took several retries before the request was accepted, having
to back off for more than 4 seconds in some cases.
At worst, the existing short back-off may make things worse (the overly
aggressive retry might cause other concurrent calls to also be rate-limited).
At best, the short back-off just isn't long enough so that particular VM
provisioning fails. For example, if AWS uses a leaky bucket algorithm [3] then
hopefully some requests would keep on getting through. But AWS don't publicise
such details of their algorithm/implementation, I believe.
[1] https://issues.apache.org/jira/browse/BROOKLYN-394
[2]
https://github.com/jclouds/jclouds/blob/rel/jclouds-2.0.0/core/src/main/java/org/jclouds/http/handlers/BackoffLimitedRetryHandler.java#L81-#L87
[3] http://en.wikipedia.org/wiki/Leaky_bucket
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