Zaqar/specs/api/next
Marconi API - Next
Brainstorming page for API improvements. The ideas below need to be discussed with the Marconi team and the OS community. They will be turned into blueprints as appropriate.
Generic
-
Auto-generate client UUID if not given- Makes things more confusing, since
- Clearly define whether client ID is required for every request, and enforce it in the implementation
- Always require it, and log the id in every log line for tracing, analytics, support, etc.
- Plan for v1.1
-
Consider allowing opaque string for client ID rather than UUID (will need to understand what else people want to use?)- it isn't *that* hard to generate one
- saying it has to be uuid makes validation easier, and reduces confusion
- Remove deprecated "partial results" semantics from message posting
- This is no longer a possiblity with the mongo driver, and other backends probably don't need it either
- Simplifies client implementations
- Plan for v1.1
- Include claim information when listing messages and retrieving individual messages
- Include Client ID in claim data
- Helps when auditing a queue, diagnostics?
- Extra storage is trivial when storing UUID as binary (16 bytes)
- Plan tentatively for v1.1 - need to think more about use cases
-
List claims for a given queue- Worker should be able to trust claim was created as expected
- Other workers should not be looking at claims they did not create
- Auditor client can list messages and see claim IDs on them if it wants to verify
- Automatically create queues the first time a message is posted to it
- Revisit for v2.0
- Metadata?
- Typos create queues? Could mitigate with an operation flag (lazy=True by default)
- Is metadata useful for a queue?
HTTP
-
Return an href for deleting all claimed messages with a single call- Probably an anti-pattern, since processing multiple messages before deleting only increases the chance for orphaned messages when a worker crashes.
- If this is for perf reasons, let's solve that with alternate transports instead (persistent connections with small operation payloads, so N individual delete operations is really fast)
-
Allow PUTing metadata when creating a queue- We made it a separate resource since later we want the queue resource itself to just have options, such as default TTL (metadata != queue properties)
-
Set queue options for defaults, such as message and claim TTL.- Clients can just implement defaults instead?
- Would require caching to make fast, but still takes a little time to check.
- homedoc should return relative URIs or encode version in href-template
- Fix this in v1.0 - well-behaved "follow-your-nose" clients are broken at the moment
- https://bugs.launchpad.net/marconi/+bug/1245656
- 204 vs. 200 + empty array (e.g., when listing messages and queues, and claiming messages)
- Current behavior: https://wiki.openstack.org/wiki/Marconi/specs/api/v1#List_Messages
- while 204 isn't necessarily incorrect, and saves a few bytes on the wire, it is inconsistent with other OpenStack APIs
- may make client implementations a tad bit easier
- Plan for v1.1
- Consistency around response envelope for /messages vs /messages?ids
- Make it a different resource so the distinction between the operations is more clear
- Plan for v2
- Response envelopes in general - don't return raw arrays (to allow for extensions)
- [] ===> {"things":[]}
- Plan for v1.1
- Q. Should this also apply to request bodies, i.e., posting messages?
-
Return full URIs in location/content-location headers (rather than relative ones)- Repose doesn't (yet) support partial URIs in headers - it tries to parse them rather than just passing them through
- Clients don't have any trouble, and other rproxies don't seem to care.
- Is content-location header really necessary?
- it is really only helpful if you have alternate representations of a resource that can be accessed using a different path vs. specifying the media type in Accept
- Don't set this header any more - save a few bytes on the wire, and it isn't useful
- Plan for v1.1
- Polling model is based on the assumption of a "streaming" interaction model. Is there a place for a "point in time" listing model, where you don't always get a "next" href?
- Revisit when planning v2
- Query parameters are usually considered to be "optional", and yet DELETE queues/my-queue/messages requires an "ids" parameter. Some options:
- Leave as is. See if anyone complains.
- Make "ids" optional. In this case, DELETE my-queue/messages would be defined to delete all messages in the queue. See also: https://blueprints.launchpad.net/marconi/+spec/flush-queue
- Allow lists of id’s in the path, such as my-queue/messages/1,2,3. We experimented with this is an early API draft, but a lot of people thought it looked strange/unusual, so we didn’t do it.
- Create a separate resource - may be same as one used for GET messages?ids=1,2,3
- Don’t support bulk DELETE operations on messages.
- Revisit when planning v2