39 lines
1.7 KiB
Markdown
39 lines
1.7 KiB
Markdown
# Messaging in Openstack
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## oslo_messaging
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In PCI infra, oslo_messaging is configured using:
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- rabbitmq driver for RPC server/agent communication
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- kafka and log driver for notifications (send events to third party app)
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### RPC implementation in rabbitmq
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[RPC in openstack](https://docs.openstack.org/oslo.messaging/stein/reference/rpcclient.html) is implemented using oslo_messaging library.
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!!! note "tldr"
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- rpc call()
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- blocking call to invoke a method on a topic with 1 reply expected
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- rpc cast()
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- invoke a method on a topic in 'best effort' mode without reply. If fanout=true message, is broadcasted to all topic consumers
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In rabbitmq, a message is published to a queue using an exchange/routing_key.
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Consumers are directly connected to a queue to read messages from.
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A oslo.messaging 'topic' is almost equivalent to a rabbitmq queue.
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With a rpc call, message will be sent to rabbitmq through exchange=target.exchange queue={target.topic}.{target.server}
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Response will be sent back to caller using exchange=target.exchange queue={message.reply_queue}
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With a rpc cast fanout=false, it's the same but there is no reply mechanism
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With a rpc cast fanout=true, message will be sent to rabbitmq through exchange=target.exchange queue={target.topic}_fanout
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For rpc call and rpc cast (fanout=false), we are using quorum queues (1 publisher / 1 consumer).
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For rpc cast (fanout=true), stream queues are used because it's purpose is to broadcast messages (1 publisher / N consumers).
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On startup, every server/agent declare queues they will consume from. If queue does not exist on rabbit cluster, it is created.
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It's the same for publishing part with the exchange. |