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gbaddeley
PostPosted: Tue Mar 13, 2018 4:50 pm Post subject: Retry Logic Reply with quote

Padawan

Joined: 25 Mar 2003
Posts: 1821
Location: Melbourne, Australia

Hi, I am not an experienced broker developer or administrator.

I would like to know if there are any commonly accepted patterns for designing message flows to properly handle retry, where there is an MQ input message and call to a http request / response service. If the http response is a failure that is not due to an error in the request data and the request needs to be retried, what are the best methods of handling this in the flow design?

Eg. An interface has 1,000's of input messages per day, but sometimes the http backend service is not available or times out, due to a planned outage (could be several hours) or an issue (that may last an indefinite period of time). The flow http request timeout is typically set to a few seconds.
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fjb_saper
PostPosted: Tue Mar 13, 2018 9:24 pm Post subject: Reply with quote

Grand Poobah

Joined: 18 Nov 2003
Posts: 19684
Location: LI,NY

If the outage is planned to last only a little time say less than 5 min you could choose the retry with timer nodes.

Otherwise you should have a back-out queue and the retry will be manual when the HTTP service is fixed...


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abhi_thri
PostPosted: Wed Mar 14, 2018 1:37 am Post subject: Reply with quote

Disciple

Joined: 17 Jul 2017
Posts: 180
Location: UK

Hi...there is a setting (failedMessageWaitTime ) which might be useful if you want the flow to wait for some time before retrying (eg:- if the external system is not available for a short period of time)

http://www-01.ibm.com/support/docview.wss?uid=swg1IT12662

https://www.ibm.com/support/knowledgecenter/SSMKHH_10.0.0/com.ibm.etools.mft.doc/an09140_.htm

PS: it need to be set a value other than (1000 millisecs - default one) for it to work as expected
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joebuckeye
PostPosted: Wed Mar 14, 2018 5:32 am Post subject: Reply with quote

Partisan

Joined: 24 Aug 2007
Posts: 335
Location: Columbus, OH

We've used this pattern for MQ based retries.

https://www.ibm.com/developerworks/websphere/library/techarticles/1401_soultan/1401_soultan.html

It removes the need for timer nodes.

We do not attempt to handle the wait time math like the article above does though. Too easy to screw up. We use TIMESTAMPS and INTERVALs to handle time math for us.
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gbaddeley
PostPosted: Wed Mar 14, 2018 4:07 pm Post subject: Reply with quote

Padawan

Joined: 25 Mar 2003
Posts: 1821
Location: Melbourne, Australia

Thanks for the responses so far. I will look at them. The retry needs to be automatic, reliable and not require any manual intervention.
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fjb_saper
PostPosted: Wed Mar 14, 2018 7:54 pm Post subject: Reply with quote

Grand Poobah

Joined: 18 Nov 2003
Posts: 19684
Location: LI,NY

gbaddeley wrote:
Thanks for the responses so far. I will look at them. The retry needs to be automatic, reliable and not require any manual intervention.

At best you are looking at a Fatah Morgana...(mirage...)
How can you say that the retry needs to be automatic, reliable and not require manual intervention, when you don't know the reason why or root cause of the retry behavior. Say the target system crashed. So you are going to retry millions of messages waiting for it to be fixed, and by the way nobody notified them that they crashed...
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gbaddeley
PostPosted: Thu Mar 15, 2018 3:49 pm Post subject: Reply with quote

Padawan

Joined: 25 Mar 2003
Posts: 1821
Location: Melbourne, Australia

fjb_saper wrote:
Say the target system crashed. So you are going to retry millions of messages waiting for it to be fixed, and by the way nobody notified them that they crashed...

Sorry, I am assuming that the target systems have their own monitoring and alerting, and they will actively fix issues to restore service.

On the broker side, we have alerting for MQ queue depth thresholds and messages aging, but we wouldn't be taking any action, other than checking that the target system app support team is working on the issue.
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fjb_saper
PostPosted: Thu Mar 15, 2018 8:19 pm Post subject: Reply with quote

Grand Poobah

Joined: 18 Nov 2003
Posts: 19684
Location: LI,NY

gbaddeley wrote:
fjb_saper wrote:
Say the target system crashed. So you are going to retry millions of messages waiting for it to be fixed, and by the way nobody notified them that they crashed...

Sorry, I am assuming that the target systems have their own monitoring and alerting, and they will actively fix issues to restore service.

On the broker side, we have alerting for MQ queue depth thresholds and messages aging, but we wouldn't be taking any action, other than checking that the target system app support team is working on the issue.

Your assumptions in god's ear. Alas my experience tells me otherwise.

We had a call to a .NET service (over MQ) and MQ was the first to notice deterioration in the response time when there was a problem. Sometimes all they did was recycle their .NET servers in a rolling fashion, and the world was ok again...
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Vitor
PostPosted: Fri Mar 16, 2018 5:04 am Post subject: Reply with quote

Grand High Poobah

Joined: 11 Nov 2005
Posts: 25017
Location: Ohio, USA

gbaddeley wrote:
Sorry, I am assuming that the target systems have their own monitoring and alerting, and they will actively fix issues to restore service.


Hah!



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PeterPotkay
PostPosted: Fri Mar 16, 2018 4:14 pm Post subject: Re: Retry Logic Reply with quote

Jedi Council

Joined: 15 May 2001
Posts: 7427

gbaddeley wrote:
Hi, I am not an experienced broker developer or administrator.

Neither am I. I struggle even qualifying as inexperienced.

gbaddeley wrote:

I would like to know if there are any commonly accepted patterns for designing message flows to properly handle retry, where there is an MQ input message and call to a http request / response service.

I'm an anonymous moron on the internet, so I can offer a smug answer: Why is this your problem? You are just a proxy for the service provider, that is having issues, that only allows a synchronous call (http), that has no answer for you, and offer no mechanism for processing your request later. "Sorry, no one's home, come back another day." I don't think its your obligation to attempt make this "better".

Just proxy the bad news right back.

The front end waits "x" seconds for your MQ reply.
At no later than x-1 seconds you should send them a reply: either a success, or details explaining the http backend is N/A - ya, know, the same thing they would be getting if they were calling the backend directly themselves.
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