zaqar/doc/source/user/headers_queue_api_working.rst

Common Headers

Each request to the Message Queuing API must include certain standard and extended HTTP headers (as shown in the following table). These headers provide host, agent, authentication, and other pertinent information to the server. The following table provides the common headers used by the API.

Header	Description
Host	Host name of the API
Date	Current date and time
Accept	Media type to use. Initially, only application/json is supported. Note: The "Accept" header is required.
Accept-Encoding	Specifies that the agent accepts gzip-encoded response bodies
Content-Type	application/json
Content-Length	For POST or PUT requests, the length in bytes of the message document being submitted
X-Auth-Token	Authorization token
X-Project-Id	An ID for a project to which the value of X-Auth-Token grants access. Queues are created under this project. The project ID is the same as the account ID (also sometimes called tenant ID).
Client-ID	A UUID for each client instance. The UUID must be submitted in its canonical form (for example, 3381af92-2b9e-11e3-b191-71861300734c). The client generates the Client-ID once. Client-ID persists between restarts of the client so the client should reuse that same Client-ID.

Note: All message-related operations require the use of "Client-ID" in the headers to ensure that messages are not echoed back to the client that posted them, unless the client explicitly requests this.

Working with the Message Queuing API

This chapter contains a simple exercise with some basic Message Queuing requests that you will commonly use. Example requests are provided in cURL, followed by the response.

For a complete list of operations available for Message Queuing, see getting_started Each operation is fully described in the Message Queuing API v2 Reference.

Create Queue

The Create Queue operation creates a queue in the region of your choice.

The body of the PUT request is empty.

The template is as follows:

PUT {endpoint}/queues/{queue_name}

The queue_name parameter specifies the name to give the queue. The name must not exceed 64 bytes in length and is limited to US-ASCII letters, digits, underscores, and hyphens.

Following are examples of a Create Queue request and response:

curl -i -X PUT https://queues.api.openstack.org/v2/queues/samplequeue \
-H "X-Auth-Token: " \
-H "Accept: application/json" \
-H "X-Project-Id: "

HTTP/1.1 201 Created
Content-Length: 0
Location: /v2/queues/samplequeue

Post Message

The Post Message operation inserts one or more messages in a queue.

You can submit up to 10 messages in a single request, but you must encapsulate them in a collection container (an array in JSON, even for a single message - without the JSON array, you receive an "Invalid body request" error message). You can use the resulting value of the location header or response body to retrieve the created messages for further processing if needed.

The template is as follows:

POST {endpoint}/queues/{queue_name}/messages

The client specifies only the body and ttl attributes for the message. Metadata, such as id and age, is added.

The response body contains a list of resource paths that correspond to each message submitted in the request, in the same order as they were submitted.

If a server-side error occurs during the processing of the submitted messages, a partial list is returned. The partial attribute is set to true, and the client tries to post the remaining messages again.

Important

The partial attribute has been deprecated in the v1.0 API and is not available in the v1.1 API. Drivers are now required to operate in a transactional manner. In other words, either all messages must be posted, or none of them.

The body attribute specifies an arbitrary document that constitutes the body of the message being sent.

The following rules apply for the maximum size:

• The size is limited to 256 KB for the entire request body (as-is), including whitespace.
• The maximum size of posted messages is the maximum size of the entire request document (rather than the sum of the individual message body field values as it was earlier releases). On error, the client is notified of by how much the request exceeded the limit.

The document must be valid JSON. (The Message Queuing service validates it.)

The ttl attribute specifies the lifetime of the message. When the lifetime expires, the server deletes the message and removes it from the queue. Valid values are 60 through 1209600 seconds (14 days).

Note

The server might not actually delete the message until its age reaches (ttl + 60) seconds. So there might be a delay of 60 seconds after the message expires before it is deleted.

The following are examples of a Post Message request and response:

curl -i -X POST https://queues.api.openstack.org/v1/queues/samplequeue/messages -d \
'[{"ttl": 300,"body": {"event": "BackupStarted"}},{"ttl": 60,"body": {"play": "hockey"}}]' \
-H "Content-type: application/json" \
-H "Client-ID: e58668fc-26eb-11e3-8270-5b3128d43830" \
-H "X-Auth-Token: " \
-H "Accept: application/json" \
-H "X-Project-Id: "

HTTP/1.1 201 Created
Content-Length: 153
Content-Type: application/json; charset=utf-8
Location: /v1/queues/samplequeue/messages?ids=51ca00a0c508f154c912b85c,51ca00a0c508f154c912b85d

{"partial": false, "resources": ["/v1/queues/samplequeue/messages/51ca00a0c508f154c912b85c", "/v1/queues/samplequeue/messages/51ca00a0c508f154c912b85d"]}

Claim Messages

The Claim Messages operation claims a set of messages (up to the value of the limit parameter) from oldest to newest and skips any messages that are already claimed. If there are no messages available to claim, the Message Queuing service returns an HTTP 204 No Content response code.

The template is as follows:

POST {endpoint}/queues/{queue_name}/claims{?limit}
Content-Type: application/json

{
    "ttl": {claim_ttl},
    "grace": {message_grace}
}

The client (worker) needs to delete the message when it has finished processing it. The client deletes the message before the claim expires to ensure that the message is processed only once. If a client needs more time, the Cloud Service provides the Update Claim operation to make changes. See the Message Queuing API v1 Reference for a description of this operation. As part of the delete operation, workers specify the claim ID (which is best done by simply using the provided href). If workers perform these actions, then if a claim simply expires, the server can return an error and notify the worker of a possible race condition. This action gives the worker a chance to roll back its own processing of the given message because another worker can claim the message and process it.

The age given for a claim is relative to the server's clock. The claim's age is useful for determining how quickly messages are getting processed and whether a given message's claim is about to expire.

When a claim expires, it is released back to the queue for other workers to claim. (If the original worker failed to process the message, another client worker can then claim the message.)

The limit parameter specifies the number of messages to claim. The limit parameter is configurable. The default is 20. Messages are claimed based on the number of messages available. The server might claim and return less than the requested number of messages.

The ttl attribute specifies the lifetime of the claim. While messages are claimed, they are not available to other workers. The value must be between 60 and 43200 seconds (12 hours).

The grace attribute specifies the message grace period in seconds. Valid values are between 60 and 43200 seconds (12 hours). To deal with workers that have stopped responding (for up to 1209600 seconds or 14 days, including claim lifetime), the server extends the lifetime of claimed messages to be at least as long as the lifetime of the claim itself, plus the specified grace period. If a claimed message normally lives longer than the grace period, its expiration is not adjusted. it

Following are examples of a Claim Messages request and response:

curl -i -X POST https://queues.api.openstack.org/v1/queues/samplequeue/claims -d \
'{"ttl": 300,"grace":300}' \
-H "Content-type: application/json" \
-H "Client-ID: e58668fc-26eb-11e3-8270-5b3128d43830" \
-H "X-Auth-Token: " \
-H "Accept: application/json" \
-H "X-Project-Id: "

HTTP/1.1 201 OK
Content-Length: 164
Content-Type: application/json; charset=utf-8
Location: /v1/queues/samplequeue/claims/51ca011c821e7250f344efd6
X-Project-Id:

[
  {
    "body": {
      "event": "BackupStarted"
    },
    "age": 124,
    "href": "\/v1\/queues\/samplequeue\/messages\/51ca00a0c508f154c912b85c?claim_id=51ca011c821e7250f344efd6",
    "ttl": 300
  }
]

Delete Message with Claim ID

The Delete Message operations deletes messages.

The template is as follows:

DELETE {endpoint}/queues/{queue_name}/messages/{message_id}{?claim_id}

The message_id parameter specifies the message to delete.

The claim_id parameter specifies that the message is deleted only if it has the specified claim ID and that claim has not expired. This specification is useful for ensuring that only one worker processes any given message. When a worker's claim expires before it deletes a message that it has processed, the worker must roll back any actions it took based on that message because another worker can now claim and process the same message.

Following are examples of a Delete Message request and response:

curl -i -X DELETE https://queues.api.openstack.org/v1/queues/samplequeue/messages/51ca00a0c508f154c912b85c?claim_id=51ca011c821e7250f344efd6 \
-H "Content-type: application/json" \
-H "X-Auth-Token: " \
-H "Client-ID: e58668fc-26eb-11e3-8270-5b3128d43830" \
-H "Accept: application/json" \
-H "X-Project-Id: "

HTTP/1.1 204 No Content

Release Claim

The Release Claim operation immediately releases a claim, making any remaining, undeleted) messages associated with the claim available to other workers.

The template is as follows:

DELETE {endpoint}/queues/{queue_name}/claims/{claim_id}

This operation is useful when a worker is performing a graceful shutdown, fails to process one or more messages, or is taking longer than expected to process messages and wants to make the remainder of the messages available to other workers.

Following are examples of a Release Claim request and response:

curl -i -X DELETE https://queues.api.openstack.org/v1/queues/samplequeue/claims/51ca011c821e7250f344efd6 \
-H "Content-type: application/json" \
-H "X-Auth-Token: " \
-H "Client-ID: e58668fc-26eb-11e3-8270-5b3128d43830"  \
-H "Accept: application/json" \
-H "X-Project-Id: "

HTTP/1.1 204 No Content

Delete Queue

The Delete Queue operation immediately deletes a queue and all of its existing messages.

The template is as follows:

DELETE {endpoint}/queues/{queue_name}

Following are examples of a Delete Queue request and response:

curl -i -X DELETE https://queues.api.openstack.org/v1/queues/samplequeue \
-H "Content-type: application/json" \
-H "X-Auth-Token: " \
-H "Accept: application/json" \
-H "X-Project-Id: "

HTTP/1.1 204 No Content