Set up a producer-consumer model with Cloud Queues

  • Last updated on: 2016-05-09
  • Authored by: Megan Meza

Setting up a Producer-Consumer model in Cloud Queues consists of posting messages to your queue, consumers claiming messages from that queue, and then deleting the completed message.

The producer-consumer mode has the following characteristics:

  • Messages are acted upon by one (and only one) worker.
  • Worker must delete message when done.
  • TTL restores message to unclaimed state if worker never finishes.
  • Ideal for dispatching jobs to multiple processors.

This mode is ideal for dispatching jobs to multiple processors.

Post messages to a queue

Queues support posting 10 messages at the same time. The following cURL command posts two messages within the same request:

$ curl -i -X POST https://$ENDPOINT:443/v1/queues/samplequeue/messages \
-d '[{"ttl": 300, "body": {"event": "two"}}, {"ttl": 60, "body": {"event": "three"}}]' \
-H "Content-type: application/json" \
-H "Client-ID: e58668fc-26eb-11e3-8270-5b3128d43830" \
-H "X-Auth-Token: $TOKEN"

Note: Use Claim TTLs to protect from agent/client failure while they have a message claimed. In the event that a server goes offline and cannot complete the message it has claimed, the claim TTL will expire and that message will be returned to the queue for other consumers or workers to claim.

The response should look similar to the following:

HTTP/1.1 201 Created     
Content-Length: 153     
Content-Type: application/json; charset=utf-8     
Location: /v1/queues/samplequeue/messages?ids=51e840e71d10b2055fd565fb,51e840e71d10b2055fd565fc{partial": false, "resources": ["/v1/queues/samplequeue/messages/51e840e71d10b2055fd565fb", "/v1/queues/samplequeue/messages/51e840e71d10b2055fd565fc"]}

In the response, you can see that the queue returned two IDs. It is always a good practice to post messages in batches as network latency will be a smaller factor in overall performance compared to sending one message at a time.

Claim messages

Claiming a message is similar to marking a message so that it will be invisible when another worker wants to claim messages. Cloud Queues claims 10 messages by default.

The following cURL command limits the number of claims to two:

$ curl -i -X POST https://\
$ENDPOINT:443/v1/queues/samplequeue/claims?limit=2 -d ' { "ttl": 60, "grace": 60} '\
-H "X-Auth-Token: $TOKEN" \
-H "Content-type: application/json" -H "Client-ID: e58668fc-26eb-11e3-8270-5b3128d43830"

The response should look similar to the following. Note that there are only two messages returned because of the limit used in the request.

HTTP/1.1 200 OK Content-Length: 306
Content-Type: application/json; charset=utf-8
Location: /v1/queues/samplequeue/claims/51e852d01d10b2056dd5703c [{"body": {"event": "two"}, "age": 5,         "href":"/v1/queues/samplequeue/messages/51e852cb1d10b20571d56f10?claim_id=51e852d01d10b2056dd5703c",
"ttl": 300}, {"body": {"event": "three"}, "age": 5, "href":
"/v1/queues/samplequeue/messages/51e852cb1d10b20571d56f11?claim_id=51e852d01d10b2056dd5703c",
"ttl": 120}]

Delete messages

The following cURL command deletes messages that have been processed by a worker:

$ curl -i -X DELETE $API_ENDPOINT/queues/samplequeue/messages/51ca00a0c508f154c912b85c?claim_id=51ca011c821e7250f344efd6 \
-H "Content-type: application/json" \
-H "X-Auth-Token: $AUTH_TOKEN" \
-H "Client-ID: e58668fc-26eb-11e3-8270-5b3128d43830" \
-H "Accept: application/json" \
-H "X-Project-Id: $TENANT_ID"

The response should look similar to the following:

HTTP/1.1 204 No Content

204 No Content validates that there are no existing messages with the given message and claim id. However, it doesn’t necessarily indicate that message is deleted.

For additional API documentations, see the following resources:

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