add pattern - role:transport,type:balance,get:stats

[rjrodger]

the balance-client should collect performance stats on the health of targets, this can then be used to implement circuit breakers etc

[cjihrig]

Is this implemented anywhere else that I can use as a reference?

[mcollina]

@cjihrig regarding health, I don't think so. Mainly because we need to define what is health for a target.

I would say that the only metric that is available is "number of messages sent but not replied to" a given target. Not sure how to get it in a non obtrusive way (and without a perf hit).

[rjrodger]

As a quick win, you can repurpose the rolling-stats module as used in Seneca main and use it in the same way to count and time messages responses:
https://github.com/rjrodger/rolling-stats
https://github.com/senecajs/seneca/blob/master/seneca.js#L1068
/cc @geek

What you will need to figure out is how to handle:

• primary pin may be a glob, so you need to capture on args.meta$.pattern to get the concrete pattern
• different target lifetimes - a target at a particular location (ip and port) is actually a series of temporal incarnations (restarts, updated deployments, change of underlying AWS instance, etc, etc), so identity cannot just be expressed by location

/cc @mcdonnelldean it should be possible to capture and chart this data into the dashboard - consider how you would want to do that

@cjihrig the purpose of the get:stats pattern is to provide information to balancing strategies - e.g reduce load on slow service etc

[rjrodger]

@cjihrig it would help you a lot to run through the nodezoo workshop: https://github.com/rjrodger/nodezoo

in particular, you can add balancing scenarios:

• have multiple search services and use the balance-client over them, actor model
• have multiple npm and git services, publish model (who cares if they perform the same work twice! redundancy ftw :) )

[mcdonnelldean]

@cjihrig We should probably talk in the new year on this too. I have some examples of charting similar info I want to show you for context.

[mcdonnelldean]

@rjrodger I might close and reframe this. There is a lot of could ideas in this. I have someone in mind but I think there are a lot of details we could pull out of this. I would be super interested to know the round robin stats for a particular service for instance.

For now I've added enhancement but this is something I definitely want to explore as I don't think we take nearly as much advantage of these sorts of patterns as we can and should.

[dgonzalez]

Hi @mcdonnelldean. I am working in something related to stats and circuit breaking and I am actually modifying now seneca-balance-client (I have done it but I am trying to debug a tricky error) to introduce circuit breaking capabilities as well as stats collection. I think it might be worth having a talk to brainstorm ideas.

[mcdonnelldean]

For sure, I am out all this week but let's catch up when I get back.

[dgonzalez]

Perfecto. I'll put something down in the diary.

[mcdonnelldean]

Do, send me on a calendar invite. @mcollina yourself or Dave may want to sit in on this each to see what sort of stats are being emitted?

[dgonzalez]

Yup. Id like to sit in there. I have a branch already with something going
on. Ill send the invite.
On 26 Apr 2016 12:12 p.m., "Dean McDonnell" notifications@github.com
wrote:

Do, send me on a calendar invite. @mcollina https://github.com/mcollina
yourself or Dave may want to sit in on this each to see what sort of stats
are being emitted?

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