fedora-messaging

Synopsis

fedora-messaging COMMAND [OPTIONS] [ARGS]…

Description

fedora-messaging can be used to work with AMQP message brokers using the fedora-messaging library to start message consumers.

Options

--help

Show help text and exit.

--conf

Path to a valid configuration file to use in place of the configuration in /etc/fedora-messaging/config.toml.

Commands

There are three sub-commands, consume, publish and record, described in detail in their own sections below.

fedora-messaging consume [OPTIONS]

Starts a consumer process with a user-provided callback function to execute when a message arrives.

fedora-messaging publish [OPTIONS] FILE

Loads serialized messages from a file and publishes them to the specified exchange.

fedora-messaging record [OPTIONS] FILE

Records messages arrived from AMQP queue and saves them to file with specified name.

consume

All options below correspond to settings in the configuration file. However, not all available configuration keys can be overridden with options, so it is recommended that for complex setups and production environments you use the configuration file and no options on the command line.

--app-name

The name of the application, used by the AMQP client to identify itself to the broker. This is purely for administrator convenience to determine what applications are connected and own particular resources.

This option is equivalent to the app setting in the client_properties section of the configuration file.

--callback

The Python path to the callable object to execute when a message arrives. The Python path should be in the format module.path:object_in_module and should point to either a function or a class. Consult the API documentation for the interface required for these objects.

This option is equivalent to the callback setting in the configuration file.

--routing-key

The AMQP routing key to use with the queue. This controls what messages are delivered to the consumer. Can be specified multiple times; any message that matches at least one will be placed in the message queue.

Setting this option is equivalent to setting the routing_keys setting in all bindings entries in the configuration file.

--queue-name

The name of the message queue in AMQP. Can contain ASCII letters, digits, hyphen, underscore, period, or colon. If one is not specified, a unique name will be created for you.

Setting this option is equivalent to setting the queue setting in all bindings entries and creating a queue.<queue-name> section in the configuration file.

--exchange

The name of the exchange to bind the queue to. Can contain ASCII letters, digits, hyphen, underscore, period, or colon.

Setting this option is equivalent to setting the exchange setting in all bindings entries in the configuration file.

publish

The publish command expects the message or messages provided in FILE to be JSON objects with each message separated by a newline character. The JSON object is described by the following JSON schema:

{
  "$schema": "http://json-schema.org/draft-04/schema#",
  "description": "Schema for the JSON object used to represent messages in a file",
  "type": "object",
  "properties": {
      "topic": {"type": "string", "description": "The message topic"},
      "headers": {
          "type": "object",
          "properties": Message.headers_schema["properties"],
          "description": "The message headers",
      },
      "id": {"type": "string", "description": "The message's UUID."},
      "body": {"type": "object", "description": "The message body."},
      "queue": {
          "type": "string",
          "description": "The queue the message arrived on, if any.",
      },
  },
  "required": ["topic", "headers", "id", "body", "queue"],
}

They can be produced from Message objects by the fedora_messaging.api.dumps() API. stdin can be used instead of a file by providing - as an argument:

$ fedora-messaging publish -

Options

--exchange

The name of the exchange to publish to. Can contain ASCII letters, digits, hyphen, underscore, period, or colon.

record

--limit

The maximum number of messages to record.

--app-name

The name of the application, used by the AMQP client to identify itself to the broker. This is purely for administrator convenience to determine what applications are connected and own particular resources. If not specified, the default is recorder.

This option is equivalent to the app setting in the client_properties section of the configuration file.

--routing-key

The AMQP routing key to use with the queue. This controls what messages are delivered to the consumer. Can be specified multiple times; any message that matches at least one will be placed in the message queue.

Setting this option is equivalent to setting the routing_keys setting in all bindings entries in the configuration file.

--queue-name

The name of the message queue in AMQP. Can contain ASCII letters, digits, hyphen, underscore, period, or colon. If one is not specified, a unique name will be created for you.

Setting this option is equivalent to setting the queue setting in all bindings entries and creating a queue.<queue-name> section in the configuration file.

--exchange

The name of the exchange to bind the queue to. Can contain ASCII letters, digits, hyphen, underscore, period, or colon.

Setting this option is equivalent to setting the exchange setting in all bindings entries in the configuration file.

Exit codes

consume

The consume command can exit for a number of reasons:

0

The consumer intentionally halted by raising a HaltConsumer exception.

2

The argument or option provided is invalid.

10

The consumer was unable to declare an exchange, queue, or binding in the message broker. This occurs with the user does not have permission on the broker to create the object or the object already exists, but does not have the attributes the consumer expects (e.g. the consumer expects it to be a durable queue, but it is transient).

11

The consumer encounters an unexpected error while registering the consumer with the broker. This is a bug in fedora-messaging and should be reported.

12

The consumer is canceled by the message broker. The consumer is typically canceled when the queue it is subscribed to is deleted on the broker, but other exceptional cases could result in this. The broker administrators should be consulted in this case.

13

An unexpected general exception is raised by your consumer callback.

Additionally, consumer callbacks can cause the command to exit with a custom exit code. Consult the consumer’s documentation to see what error codes it uses.

publish

0

The messages were all successfully published.

1

A general, unexpected exception occurred and the message was not successfully published.

121

The message broker rejected the message, likely due to resource constraints.

111

A connection to the broker could not be established.

Signals

consume

The consume command handles the SIGTERM and SIGINT signals by allowing any consumers which are currently processing a message to finish, acknowledging the message to the message broker, and then shutting down. Repeated SIGTERM or SIGINT signals are ignored. To halt immediately, send the SIGKILL signal; messages that are partially processed will be re-delivered when the consumer restarts.

Systemd service

The consume subcommand can be started as a system service, and Fedora Messaging provides a dynamic systemd service file.

First, create a valid Fedora Messaging configuration file in /etc/fedora-messaging/foo.toml, with the callback parameter pointing to your consuming function or class. Remember that you can use the consumer_config section for your own configuration.

Enable and start the service in systemd with the following commands:

systemctl enable fm-consumer@foo.service
systemctl start fm-consumer@foo.service

The service name after the @ and before the .service must match your filename in /etc/fedora-messaging (without the .toml suffix).

Help

If you find bugs in fedora-messaging or its man page, please file a bug report or a pull request:

https://github.com/fedora-infra/fedora-messaging

Or, if you prefer, send an email to infrastructure@fedoraproject.org with bug reports or patches.

fedora-messaging’s documentation is available online:

https://fedora-messaging.readthedocs.io/