Troubleshooting and debugging RabbitMQ applications

About this guide

This guide describes tools and strategies that help in troubleshooting and debugging applications that use RabbitMQ in general and March Hare in particular.

This work is licensed under a Creative Commons Attribution 3.0 Unported License (including images and stylesheets). The source is available on Github.

What version of March Hare does this guide cover?

This guide covers March Hare 2.8 and later versions.

First steps

Whenever something doesn't work, check the following things before asking on the mailing list:

  • RabbitMQ log.
  • List of users in a particular vhost you are trying to connect.
  • Network connectivity, firewall settings, DNS host resolution.

Inspecting RabbitMQ log file

In this section we will cover typical problems that can be tracked down by reading RabbitMQ log.

RabbitMQ logs abrupt TCP connection failures, timeouts, protocol version mismatches and so on. If you are running RabbitMQ, log file location depends on the operating systems and installation method. See RabbitMQ installation guide for more information.

OS X with Homebrew

On Mac OS X, RabbitMQ installed via Homebrew logs to $HOMEBREW_HOME/var/log/rabbitmq/rabbit@$HOSTNAME.log. For example, if you have Homebrew installed at /usr/local and your hostname is giove, the log will be at /usr/local/var/log/rabbitmq/rabbit@giove.log.

Authentication Failures

Here is what authentication failure looks like in a RabbitMQ log:

=ERROR REPORT==== 12-Jul-2013::16:49:03 ===
closing AMQP connection <0.31567.1> (127.0.0.1:50458 -> 127.0.0.1:5672):
{handshake_error,starting,0,
                 {amqp_error,access_refused,
                             "PLAIN login refused: user 'pipeline_agent' - invalid credentials",
                             'connection.start_ok'}}

This means that the connection attempt with the username pipeline_agent failed because the credentials were invalid. If you are seeing this message, make sure username, password and vhost are correct.

The following entry:

=ERROR REPORT==== 17-May-2011::17:26:28 ===
exception on TCP connection <0.4201.62> from 10.8.0.30:57990
{bad_header,<<65,77,81,80,0,0,9,1>>}

means that an old RabbitMQ version (pre-2.0) is used. Those versions are not supported by March Hare 0.9+. It is recommended to use the latest stable release.

March Hare will raise MarchHare::PossibleAuthenticationFailureError in such cases.

Handling Channel-level Exceptions

A broad range of problems result in AMQP channel exceptions: an indication by the broker that there was an issue that the application needs to be aware of. Channel-level exceptions are typically not fatal and can be recovered from. Some examples are:

  • Exchange is re-declared with attributes different from the original declaration. For example, a non-durable exchange is being re-declared as durable.
  • Queue is re-declared with attributes different from the original declaration. For example, an auto-deletable queue is being re-declared as non-auto-deletable.
  • Queue is bound to an exchange that does not exist.

and so on. These will result in a reasonably descriptive exception that subclasses MarchHare::ChannelLevelException. Handling and logging them will likely reveal an issue when it arises.

Testing Network Connection with RabbitMQ using Telnet

One simple way to check network connection between a particular network node and a RabbitMQ node is to use telnet:

telnet [host or ip] 5672

then enter any random string of text and hit Enter. RabbitMQ should immediately close down the connection. Here is an example session:

telnet localhost 5672
Connected to localhost.
Escape character is '^]'.
adjasd
AMQP    Connection closed by foreign host.

If Telnet exits after printing instead

telnet: connect to address [host or ip]: Connection refused
telnet: Unable to connect to remote host

then the connection between the machine that you are running Telnet tests on and RabbitMQ fails. This can be due to many different reasons, but it is a good idea to check these two things first:

  • Firewall configuration for port 5672 or 5671 (if TLS/SSL is used)
  • DNS resolution (if hostname is used)

RabbitMQ Startup Issues

Missing erlang-os-mon on Debian and Ubuntu

The following error on RabbitMQ startup on Debian or Ubuntu

ERROR: failed to load application os_mon: {"no such file or directory","os_mon.app"}

suggests that the erlang-os-mon package is not installed.

asn1 Issue on Erlang R16B01

BOOT FAILED
===========

Error description:
    {error,{cannot_start_application,public_key,{not_started,asn1}}}

is an issue in RabbitMQ 3.1 on Erlang R16B01+. It is resolved in RabbitMQ 3.1.2 and later versions.