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diff --git a/posts/2013-01-28-let-s-talk-about-graphite.org b/posts/2013-01-28-let-s-talk-about-graphite.org deleted file mode 100644 index b0e96d7..0000000 --- a/posts/2013-01-28-let-s-talk-about-graphite.org +++ /dev/null @@ -1,184 +0,0 @@ -As I've already mentionned in a [[/carbons-manhole/][previous post]], at -[[http://saymedia.com][$work]] we are currently deploying Graphite and -the usual suspects. - -Finding articles on how to install all these tools is easy, there's -plenty of them. But what's /really/ hard to find, are stories on /how to -use them/: what's collected, how, why, how do you organize your metrics, -do you rewrite them, etc. - -What I want with this post is to start a discussion about usages, -patterns, and good practices. I'm going to share how /we/, at SAY, are -using them, and maybe this could be the start of a conversation. - -** Graphite/collectd/statsd - -We're using [[https://github.com/etsy/statsd][statsd]], -[[https://collectd.org][collectd]] -[[https://github.com/graphite-project][Graphite]] (and soon -[[http://riemann.io][Riemann]] for alerting). - -*** Retention - -Our default retention policy is: =10s:1h, 1m:7d, 15m:30d, 1h:2y=. We -don't believe that Graphite should be used for alerting: it's a tool for -looking at history and trends. - -360 points for the last hour is enough to refer to a graph when an -incident occurs. Most of the teams are releasing at least once a week, -so 1 minute definition for a week is enough to compare trends between -two releases. Then we go to a month (2 sprints) and they 2 years. We -thought at first to keep only 15 months (1year + 1 quarter to compare), -but since we have enough disk space, we decided to keep two years, -however we might decide to change that in the future. - -*** System - -We don't do anything fancy here. =collectd= is running on each host, and -then write to a central =collectd= server. - -*** Services - -For shared services (Memcached, Varnish, Apache, etc), we talk to -=statsd=. We have a Perl script named =sigmoid=, with the following -usage: - -#+BEGIN_SRC sh - Usage: ./sigmoid [<options>] <metricname> <value> - Exactly one of: - --counter (value defaults to 1) - --aggregate - --gauge - --event - --raw - - Other options: - --disable-multiplex (for statsd only) - --appname - --hostname (to log on behalf of another machine) -#+END_SRC - -This script is used by other scripts who monitor logs, status of apps, -etc. This way it's very easy for a Perl, Python, Shell script to just -call =sigmoid= via =system=, and then send the metric and the value to -=statsd=. - -For some other services we might need something more specific. Let's -take a look at Apache. We have another Perl script for the *CustomLog* -settings (=CustomLog "|/usr/local/bin/apache-statsd"=). The script is -doing the following things: - -- compute the size of the HTTP request in bytes -- compute how long it took to return the response - -Then, it will send the following lines to =statsd= (with $base being the -vhost in our case): - -- =$base.all.requests:1|c= increases the total of HTTP requests we're - receiving -- =$base.all.bytes:$bytes|ms= send the size, in bytes, of that request -- =$base.all.time:$msec|ms= the time spend to get the response - -Now we will send the same line two more times, with a different prefix: -=$base.method.$request_method= /and/ =$base.status.$status=. - -*** Applications - -Here, developers decide what they want to collect, and send the metric -to =statsd=. - -*** Events - -And finally we have events. Every time we push an application or a -configuration, we create a new event. - -** Proxying statsd - -We want metrics to be well organized, in a clear hierarchy. -[[https://github.com/obfuscurity][Jason Dixon]] wrote in a -[[http://obfuscurity.com/2012/05/Organizing-Your-Graphite-Metrics][blog -post]] that /Misaligned paths are ok/. I disagree. We're collecting more -than 100k metrics so far. If things are not well organized, it will -become quickly very difficult to find what you're looking for. - -So, here's how we organize our metrics. The first level is the -environment (PROD, CI, DEV, ...). Then we have /apps/ and /hosts/. For -the /host/ section, we group by cluster type (Hadoop cluster, Web -servers for TypePad, etc), and then you have the actual host, with all -the metrics collected. For /apps/, we have four main categories: -/aggregate/, /counters/, /events/ and /gauges/ (I'll come back on that -later). - -Earlier I said that apps where sending metrics to =statsd=, but that's -not exactly true. We (mostly) never write directly to statsd or -Graphite. - -On each host, we have a Perl script listening. This proxy will rewrite -all the incoming metrics by appending to the name the environment, the -cluster and so on. This way when someone want to send a key, he doesn't -have to care convention or using the correct prefix. - -Also, it will also multiplex the metric: we want the same key to end-up -under /host/ and under /app/. Let's take an example here. If you're -writing a web service, you may want to send a metric for the total time -taken by an endpoint (this will be an aggregate). Our key will be -something like: -*<application-name>.<endpoint-name>.<http-method>.<total-time>*. The -proxy, based on the network address, will determine that it's -environment is CI, and that it's an application. But it also knows the -name of the server, and the cluster. So two keys will be created: - -- *<CI>.<apps>.<aggregate>.<application-name>.<endpoint-name>.<http-method>.* -- *<CI>.<hosts>.<cluster-name>.<host-name>.<aggregate>.<application-name>.<endpoint-name>.<http-method>.<total-time>* - -This way we can find the metric aggregated by application, or if we -think there's a problem in one machine, we can compare per host the same -metric. - -** Other problems with statsd and Graphite - -I don't know if it's a problem with vocabulary, or our maths (I admit -that my maths are not good, but I trust Abe and Hachi's maths), but you -can't imagine how much time we spend debating around the words gauges, -counters and aggregates. What they mean, how they work, when to use -them. So here's my questions: are we missing something obvious? do we -over think it? or is it also confusing, and people are misusing them? - -Let's take *gauge* as an example. If you read -[[https://github.com/etsy/statsd/blob/master/README.md#gauges][the -documentation for gauges]], it seems very simple: you send a value, and -it will be recorded. Well, the thing is it will record only the last -value send during the 10 seconds interval. This work well when you have -a cron job that will look at something every minute and report a metric -to =statsd=, not if you're sending that 10 times a second (and yes, we -will provide a patch for documentation soon). - -Another one where we lost a good amount of time: if you're smallest -retention is different from the interval used by statsd to flush the -data, they will be graphed incorrectly (see this -[[https://github.com/etsy/statsd/issues/32#issuecomment-1830985][comment]]). - -The best "documentation" for =statsd=, so far, are the discussions in -the [[https://github.com/etsy/statsd/issues][issues]]. - -We have some other complains about Graphite. Even after reading the -[[http://graphite.wikidot.com/whisper#toc1][rationals]] for Whisper, I'm -not convinced it was a good idea to replace RRD with it. We also -discovered some issues with -[[http://if.andonlyif.net/blog/2013/01/graphites-derivative-function-lies.html][Graphite's -functions]]. - -** Meetup - -We've a huge basement at work that can be used to host meetup. There's -already a few meetup in the San Francisco about "devops" stuff -([[http://www.meetup.com/San-Francisco-Metrics-Meetup/events/98875712/][Metrics -Meetup]], [[http://www.meetup.com/San-Francisco-DevOps/][SF DevOps]], -etc), but maybe there's room for another one with a different format. - -What I would like, is a kind of forum, where a topic is picked, and -people share their /experiences/ (the bad, the good and the ugly), not -how to configure or deploy something. And there's a lot of topics where -I've questions: deployment (this will be the topic of my next entry I -think), monitoring, alerting, post-mortem, etc. If you're interested, -send me an email, or drop a comment on this post. |