Federated Message Bus¶
Some time ago, the Fedora Infrastructure team wanted to hook all the services in Fedora Infrastructure up to send messages to one another over a message bus instead of communicating with each other in the heterogenous, “Rube-Goldberg” way they did previously.
fedmsg
(FEDerated MeSsaGe bus) is a python package and API defining a brokerless
messaging architecture to send and receive messages to and from applications.
See Overview for a thorough introduction.
While originally specific to Fedora, the expansion of the project’s name was changed away from the old “Fedora Messaging” to the current “Federated Message Bus” after it was also adopted for use in Debian’s infrastructure.
Click here to see a feed of the Fedora bus. There’s also a
#fedora-fedmsg
channel on the freenode network with a firehose bot echoing
messages to channel to help give you a feel for what’s going on.
You can find the list of available topics in Fedora’s infrastructure at https://fedora-fedmsg.readthedocs.io
Receiving Messages with Python¶
import fedmsg
# Yield messages as they're available from a generator
for name, endpoint, topic, msg in fedmsg.tail_messages():
print topic, msg
Receiving Messages from the Shell¶
$ fedmsg-tail --really-pretty
Publishing Messages with Python¶
See Development on setting up your environment and workflow.
In a default configuration, sending a message looks like the following:
import fedmsg
fedmsg.publish(topic='testing', modname='test', msg={
'test': "Hello World",
})
Note
The endpoints.py
file should have an entry as "<myprogram>.<myhost>": [ ... ]
where myprogram
is
the name of the program sending the message (can be __main__
if it is a simple script) and myhost
is the
machine sending the program (corresponds to the output of hostname -s
).
If you need to publish to a specific endpoint or need a consistent endpoint, you’ll need to pass the name
parameter
and adjust the endpoints.py
accordingly.
import fedmsg
fedmsg.publish(name='mybus', topic='testing', modname='test', msg={
'test': "Hello World",
})
Note
The endpoints.py
file should have an entry as "mybus": [ ... ]
Publishing Messages from the Shell¶
$ echo "Hello World." | fedmsg-logger --modname=git --topic=repo.update
$ echo '{"a": 1}' | fedmsg-logger --json-input
$ fedmsg-logger --message="This is a message."
$ fedmsg-logger --message='{"a": 1}' --json-input
Testimonials¶
- Jordan Sissel – “Cool idea, gives new meaning to open infrastructure.”
- David Gay – “It’s like I’m working with software made by people who thought about the future.”
Community¶
The source for this document can be found on github. The issue tracker can be found there, too.
Almost all discussion happens in #fedora-apps
on the freenode network.
There is also a mailing list.
Table of Contents¶
- Overview
- Bus Topology
- Frequently Asked Questions
- Development
- Deploying fedmsg for yourself
- Commands
- Python API: Emitting Messages
- Python API: Consuming Messages
- Message Encoding – JSON
- Cryptography and Message Signing
- Replay
- “Natural Language” Representation of Messages
- Compatibility with Other Messaging Technologies
- Configuration
- List of Message Topics
Note
Proposal - Fedora Messaging with 0mq (fedmsg) is a now out-moded document, but is kept here for historical purposes.