Heroku router errors H13 logged by LogEntries

Question

I'm trying to figure out whether these errors I get on a regular basis from LogEntries are worth worrying about. I have an iPhone app that talks to a Rails API on heroku. I use HireFire to automatically increase and decrease the number of dynos and workers the application needs.

I presume these erros are being caused by the dynos scaling down and then something making a call to that dyno and therefore causing the H13 error. If so, is there a way to stop this? Surely user requests would not go to a dyno that no longer existed?

Here are the most common logs I've been getting in context:

1.

2012-10-18 10:01:15.170 209 <13>1 2012-10-18T10:01:14+00:00 app web.1 - - Started GET "/hirefireapp/xxxxxxxxxxxxxxxx/info" for 23.22.73.241 at Thu Oct 18 03:01:14 -0700 2012
2012-10-18 10:01:15.170 162 <13>1 2012-10-18T10:01:14+00:00 app web.1 - - cache: [GET /hirefireapp/xxxxxxxxxxxxxxxx/info] miss
2012-10-18 10:01:22.147 146 <13>1 2012-10-18T10:01:22+00:00 app web.2 - - Connected to NewRelic Service at collector-2.newrelic.com:80
2012-10-18 10:01:22.308 217 <13>1 2012-10-18T10:01:22+00:00 app web.2 - - ** [NewRelic][10/18/12 03:01:22 -0700 xxxxxxxxxxxxxxxx (2)] INFO : Reporting performance data every 60 seconds.
2012-10-18 10:01:38.118 86 <13>1 2012-10-18T10:01:38+00:00 app web.2 - -
2012-10-18 10:01:38.212 86 <13>1 2012-10-18T10:01:38+00:00 app web.2 - -
2012-10-18 10:01:38.212 154 <13>1 2012-10-18T10:01:38+00:00 app web.2 - - Started GET "/" for 204.93.223.151 at Thu Oct 18 03:01:38 -0700 2012
2012-10-18 10:01:38.212 128 <13>1 2012-10-18T10:01:38+00:00 app web.2 - -   Processing by CmsController#index as */*
2012-10-18 10:01:38.212 148 <13>1 2012-10-18T10:01:38+00:00 app web.2 - - Rendered cms/index.html.erb within layouts/application (4.8ms)
2012-10-18 10:01:41.291 124 <40>1 2012-10-18T10:01:41+00:00 heroku web.2 - - Stopping all processes with SIGTERM
2012-10-18 10:01:42.243 217 <158>1 2012-10-18T10:01:42+00:00 heroku router - - Error H13 (Connection closed without response) -> GET my-api.heroku.com/ dyno=web.2 queue= wait= service= status=503 bytes=

2.

2012-10-16 17:31:25.184 189 <13>1 2012-10-16T17:31:25+00:00 app web.2 - - ** [NewRelic][10/16/12 10:31:25 -0700 (2)] INFO : Dispatcher: thin
2012-10-16 17:31:25.184 197 <13>1 2012-10-16T17:31:25+00:00 app web.2 - - ** [NewRelic][10/16/12 10:31:25 -0700 (2)] INFO : Application: my-api
2012-10-16 17:31:25.184 220 <13>1 2012-10-16T17:31:25+00:00 app web.2 - - ** [NewRelic][10/16/12 10:31:25 -0700 (2)] INFO : New Relic Ruby Agent 3.3.1 Initialized: pid = 2
2012-10-16 17:31:25.585 265 <13>1 2012-10-16T17:31:25+00:00 app web.2 - - ** [NewRelic][10/16/12 10:31:25 -0700 (2)] INFO : NewRelic::Agent::Samplers::DelayedJobLockSampler sampler not available: No DJ worker present
2012-10-16 17:31:37.068 217 <13>1 2012-10-16T17:31:37+00:00 app web.2 - - ** [NewRelic][10/16/12 10:31:36 -0700 (2)] INFO : Reporting performance data every 60 seconds.
2012-10-16 17:31:39.786 86 <13>1 2012-10-16T17:31:39+00:00 app web.2 - -
2012-10-16 17:31:39.884 86 <13>1 2012-10-16T17:31:39+00:00 app web.2 - -
2012-10-16 17:31:39.884 154 <13>1 2012-10-16T17:31:39+00:00 app web.2 - - Started GET "/" for xxx.xx.xxx.xxx at Tue Oct 16 10:31:39 -0700 2012
2012-10-16 17:31:39.884 128 <13>1 2012-10-16T17:31:39+00:00 app web.2 - -   Processing by CmsController#index as */*
2012-10-16 17:31:39.981 149 <13>1 2012-10-16T17:31:39+00:00 app web.2 - - Rendered cms/index.html.erb within layouts/application (18.1ms)
2012-10-16 17:31:46.082 217 <158>1 2012-10-16T17:31:46+00:00 heroku router - - Error H13 (Connection closed without response) -> GET my-api.heroku.com/ dyno=web.2 queue= wait= service= status=503 bytes=

Any advice would be much appreciated!

Thanks Pete

Answer 1

One potential cause of the H13 issue is the Rack key space. Rack adds a protection against potential malicious attack through sending significantly large parameter keys with a HTTP request.

Rack Utils sets a limit on the key space of 65536 which may not be large enough if you are sending HTTP requests with large parameter sets.

You can change this limit by adding the following to a Rails initializer file:

if Rack::Utils.respond_to?("key_space_limit=")
  Rack::Utils.key_space_limit = 262144
end

I found this figure (4x standard) large enough to fix the H13 issues for me but you may need to test different settings based on your own personal requirements.

This may not be the cause of your particular H13 issue but it's worth checking as a possible solution.