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| == Planning Questions ==
| | #REDIRECT[[Services/Sagrada/Queuey]] |
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| What is the simplest MQ system and features to add from there?
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| *Put a single message on a queue for later retrieval in a FIFO manner, non-persistent, via a RESTful service to push and poll for messages (send XX many at once per client instruction?)
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| *Transient messages (Semi-durable, higher throughput at the possible loss of some recent messages in a crash)
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| *Persistent messages (Accessible until consumed)
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| *Prioritizing of messages? Or allow for multiple queues and have the client prioritize where it pulls messages from?
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| *Allow messages to go unacknowledged to allow a client to 'time-out' on handling it?
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| *Message push (persistent MQ connection), reduces latency but increases complexity. Pub/Sub or load-balanced on multiple connected clients?
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| Trade-offs of implementation / back-ends
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| *Non-persistent allows use of memcached for higher throughput
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| *Semi-durable allows backends that do occasional fsync's (Mongo / Redis)
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| *Fully persistent (i.e., backed by a db) would be much slower
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| Or should an App creator get to choose which characteristic they want when creating a queue?
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| i.e. someone making a real-time chat/broadcast system could choose non-persistent for lots of messages of little importance if they're missed...
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| someone sending verification emails would choose fully persistent to ensure it actually gets sent eventually
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| Crypto
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| *Payload could be encrypted at the client layer
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| *If routing keys are used (RabbitMQ style brokering), those could be encrypted as well
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| Apps should be able to create both durable and temporary queues on-demand, as well as assign a TTL to a queue for temporary use.
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| Authentication
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| *maybe [[Services/AppKeys|AppKeys]] would work, depending on if only the App could send messages... might need something else if end-user clients can directly push messages via Javascript
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| Message Handling
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| *Should the MQ Service do anything beyond merely holding messages and allowing connections for their retrieval?
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| *Simplest has no built-in handling, app would need to poll MQ service for new messages
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| *Allow a message payload to contain a callback to a RESTful service (URL + POST payload)?
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| *Message TTL?
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| Queues
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| *Single default queue per App seems reasonable
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| *Multiple queues per App? Routing of messages to multiple queues based on route key like in RabbitMQ?
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| *Temporary queues for return-paths? (i.e., using a queue to farm out something then waiting for it to complete and return data)
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| Queue Workers?
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| *Introduces additional challenge of requiring Apps to have the code the worker should call for a message accessible to the MQ Worker Service
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| *Feels like a separate service from the MQ Service (though highly related)
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| *Requires worker pools on machines, worker watchers, resource monitoring, worker killers for excessive resource usage, deploying additional machines as App tasks require more task processing power under load
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| *Provide 'built-in' queue workers for delayed common tasks? i.e. sending email, update caches.
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| *Handling 'excessive resource usage' requires consistent way to determine CPU usage per task regardless of existing machine utilization, kill workers that use more than XXX RSS memory, etc.
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| Introspection / Administration
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| *How much should one be able to see about current queue activity? Total queues per app? Total messages in each queue? Ability to examine payload of individual message?
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| *Most basic feature-set should include some way for an App to clear/reset one of its queues
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