Deploying fedmsg

Elsewhere, the emphasis in fedmsg docs is on how to subscribe to an existing fedmsg deployment; how do I listen for koji builds from Fedora Infrastructure? This document, on the other hand, is directed at those who want to deploy fedmsg for their own systems.

This document also only goes as far as setting things up for a single machine. You typically deploy fedmsg across an infrastructure but if you just want to try it out for “proof-of-concept”, these are the docs for you.

Lastly, the emphasis here is on the practical – there will be lots of examples.


Caveat: fedmsg is deployed at a couple different sites:

  • Fedora Infrastructure
  • to some extent, Debian Infrastructure

We wrote this document much later afterwards, so, if you come across errors, or things that don’t work right. Please report it.

The basics

First install fedmsg:

$ sudo dnf install fedmsg

Now you have some fedmsg-* cli tools like fedmsg-tail and fedmsg-logger.

On Fedora systems, fedmsg is configured by default to subscribe to Fedora Infrastructure’s bus. Since you are deploying for your own site, you don’t want that. So edit /etc/fedmsg.d/ and comment out the whole “fedora-infrastructure” section, like this:

#"fedora-infrastructure": [
#    "tcp://",
#    #"tcp://",

Starting fedmsg-relay

Not all fedmsg interactions require the relay, but publishing messages from a terminal does.

Install fedmsg-relay and start it:

$ sudo dnf install fedmsg-relay
$ sudo systemctl restart fedmsg-relay
$ sudo systemctl enable fedmsg-relay

It has a pid file in /var/run/fedmsg/ and you can view the logs in journalctl --follow. On other systems you can find the logs in /var/log/fedmsg/fedmsg-relay.log.

Out of the box, it should be listening for incoming messages on tcp:// and re-publishing them indiscriminately at tcp:// It is fine to keep these defaults.

Test it out

Try a test! Open two terminals:

  • In the first, type fedmsg-tail --really-pretty
  • In the second, type echo "Hello world" | fedmsg-logger

You should see the JSON representation of your message show up in the first terminal. It should look something like this.

  "username": "root",
  "i": 1,
  "timestamp": 1393878837,
  "msg_id": "2014-f1c49f0b-5caf-49e6-b79a-cc54bcfac602",
  "topic": "",
  "msg": {
    "log": "Hello world"

These are two handy tools for debugging the configuration of your bus.

Branching out to two machines

Everything is tied together in fedmsg by the endpoints dict. It lets

  • A publishing service know what port it should be publishing on.
  • A consuming service know where the publisher is so it can connect there.

Let’s say you have two machines hostA and hostB. If you installed that fedmsg-relay on hostA as discussed above, then the config file in /etc/fedmsg.d/ is going to have values like tcp:// That address will only work for local connectivity. Try changing all occurences of in that file to hostA so that it looks something like this:

config = dict(
        "relay_outbound": [
    relay_inbound = "tcp://hostA:2003",

To confirm that something’s not immediately broken, you can go through the tests of doing fedmsg-logger and fedmsg-tail on hostA again (all “local”).

Copy that file over to hostB with scp /etc/fedmsg.d/ hostB:/etc/fedmsg.d/

You should now be able to run fedmsg-tail on hostA and have it receive a message from fedmsg-logger on hostB and vice versa have a fedmsg-tail session on hostB receive a fedmsg-logger statement from hostA.

The key here is that fedmsg works by having a shared configuration that is distributed to all machines. hostA only knows where to publish by reading in the config and hostB only knows where to consume by reading in the config. If the configs are not the same, then there’s going to be a mis-match and your messages won’t arrive… anywhere.

It’s a far leap ahead, but you’re welcome to browse the configuration we’re using in production for Fedora Infrastructure.

Store all messages

And now for a different topic.

We use a tool called datanommer to store all the messages that come across the bus in a postgres database. Using whatever relational database you like should be possible just by modifying the config.

Setting up postgres

Here, set up a postgres database:

$ sudo dnf install postgresql-server python-psycopg2
$ postgresql-setup initdb

Edit the /var/lib/pgsql/data/pg_hba.conf as the user postgres. You might find a line like this:

host all all ident sameuser
host all all ::1/128 ident sameuser

Instead of that line, change it to this:

host all all trust
host all all ::1/128 trust


Using trust is super unsafe long term. That means that anyone with any password will be able to connect locally. That’s fine for our little one-box test here, but you’ll want to use md5 or kerberos or something long term.

Start up postgres:

$ systemctl start postgresql
$ systemctl enable postgresql

Create a database user and the db itself for datanommer and friends:

$ sudo -u postgres createuser -SDRPE datanommer
$ sudo -u postgres createdb -E utf8 datanommer -O datanommer

Setting up datanommer

Install it:

$ sudo dnf install fedmsg-hub python-datanommer-consumer datanommer-commands

Edit the configuration to 1) be enabled, 2) point at your newly created postgres db. Edit /etc/fedmsg.d/ and change the whole thing to look like this:

config = {
    'datanommer.enabled': True,
    'datanommer.sqlalchemy.url': 'postgresql://datanommer:password@localhost/datanommer',

Run the following command from the datanommer-commands package to set up the tables. It will read in that connection url from /etc/fedmsg.d/

$ datanommer-create-db

Start the fedmsg-hub daemon, which will pick up the datanommer plugin, which will in turn read in that connection string, start listening for messages, and store them all in the db.

$ sudo systemctl start fedmsg-hub
$ sudo systemctl enable fedmsg-hub

You can check journalctl --follow for logs.

Try testing again with fedmsg-logger. After publishing a message, you should see it in the datanommer stats if you run datanommer-stats:

$ datanommer-stats
[2014-03-03 20:34:43][    fedmsg    INFO] logger has 2 entries

Querying datanommer with datagrepper

You can, of course, query datanommer with SQL yourself (and there’s a python API for directly querying in the datanommer.models module). For the rest here is the HTTP API we have called “datagrepper”. Let’s set it up:

$ sudo dnf install datagrepper mod_wsgi

Add a config file for it in /etc/httpd/conf.d/datagrepper.conf with these contents:

LoadModule wsgi_module modules/

# Static resources for the datagrepper app.
Alias /datagrepper/css /usr/lib/python2.7/site-packages/datagrepper/static/css

WSGIDaemonProcess datagrepper user=fedmsg group=fedmsg maximum-requests=50000 display-name=datagrepper processes=8 threads=4 inactivity-timeout=300
WSGISocketPrefix run/wsgi
WSGIRestrictStdout Off
WSGIRestrictSignal Off
WSGIPythonOptimize 1

WSGIScriptAlias /datagrepper /usr/share/datagrepper/apache/datagrepper.wsgi

<Directory /usr/share/datagrepper/>
  WSGIProcessGroup datagrepper
  # XXX - The syntax for this is different for different versions of apache
  Require all granted

Finally, start up httpd with:

$ sudo systemctl restart httpd
$ sudo systemctl enable httpd

And it should just work. Open a web browser and try to visit http://localhost/datagrepper/.

The whole point of datagrepper is its API, which you might experiment with using the httpie tool:

$ sudo dnf install httpie
$ http get http://localhost/datagrepper/raw/ order==desc


This document is a work in progress. Future topics may include selinux and Cryptography and Message Signing.

Let us know what you’d like to know if it is missing.