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ReqMgr2 MicroService Transferor

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Alan Malta Rodrigues edited this page Apr 9, 2019 · 23 revisions

This documentation is meant to describe the architecture, behaviour and APIs for the ReqMgr2 Microservice Transferor module, which is responsible for looking data up at the global workqueue level and creating PhEDEx subscriptions.

For the record - given that those abbreviations will be mentioned several times in this document - here is their meaning GQE: global workqueue element LQE: local workqueue element

Here is how we envision it to work:

  1. Unified assigns a workflow (request transition from assignment-approved to assigned)
  2. Global Workqueue queries ReqMgr2 for workflows in the assigned status. It then parses the request spec and create chunks of work GQE in the New status. Once ALL elements have been created, the request goes to the acquired status (right now it happens asynchronously with a ReqMgr2 CherryPy thread, TBD and investigated whether it's safe to keep it that way).
  3. The MicroService kicks in and queries ReqMgr2 for requests in acquired status;
  • IF there are none requests, it exits and wait until the next cycle.
  1. Otherwise, it has to fetch the Campaign(s) configuration for every request (this can be cached!), which will be used to decide how many replicas have to be made and where data has to be subscribed to.
  • IF a Campaign configuration cannot be found, then we have to create an alert and skip that workflow (leaving it in acquired status)
  1. Otherwise, given the list of requests in acquired, MicroService talks then to the Global WorkQueue and fetches all their GQE in the New status
  • If there are none, then all subscriptions have been made and the request should be soon moving to the staging status
  • Otherwise, run the Transferor algorithm - taking into account the Campaign configuration, from CouchDB - and create PhEDEx subscriptions.
  • PS.: Check whether parent blocks are available in the GQE
  1. Set the GQE status to Available for all the PhEDEx subscriptions that were successfully made (or for GQE without any input data!)
  2. TBD update the request status to staging. Or let the ReqMgr2 CherryPy thread take care of that...

The process above has to be executed for every single workflow. By design, the agents won't pull any GQE work that is still without a PhEDEx subscription (in New status).

In case a PhEDEx subscription fails, the GQE will remain in the New status, and so should the request still be in the acquired status as well.

Open questions Do we want to keep track of the subscriptions (persisting data somewhere?)?

Do we want to monitor the subscriptions and act upon issues and/or stuck transfers? Or we just assume transfers will eventually succeed? Alerts have to be created for bad input placement (bad transfers) as well.

ReqMgr2 MicroService APIs

The MicroService is a data-service which provides set of APIs to perform certain actions. Its general architecture is shown below: MicroServiceArchitecture

In particular the WMCore MicroService provides an interface to perform Unified actions, such as fetch requests from ReqMgr2 data-services, obtain necessary informations for data placement and place requests of assigned workflows into data placement system PhEDEx.

Available APIs

GET APIs

  • /microservice/data provides basic information about MicroService. It returns the following information:
{"result": [
 {"microservice": "UnifiedTransferorManager", "request": {}, "results": {"status": {}}}
]}
  • /microservice/data/status provides detailed information about requests in MicroService. It returns the following information:
curl --cert $X509_USER_CERT --key $X509_USER_KEY -X GET -H "Content-type: application/json" https://cmsweb-testbed.cern.ch/microservice/data/status

{"result": [
 {"microservice": "UnifiedTransferorManager", "request": {}, "results": {"status": {}}}
]}

POST APIs

  • /microservice/data allows to send specific request to MicroService

post request to process some state

curl -X POST -H "Content-type: application/json" -d '{"request":{"process":"assignment-approved"}}' http://localhost:8822/microservice/data

obtain results about specific workflow

curl --cert $X509_USER_CERT --key $X509_USER_KEY -X POST -H "Content-type: application/json" -d '{"request":{"task":"amaltaro_StepChain_DupOutMod_Mar2019_Validation_190322_105219_7255"}}' https://cmsweb-testbed.cern.ch/microservice/data

{"result": [
 {"amaltaro_StepChain_DupOutMod_Mar2019_Validation_190322_105219_7255": {"completed": 100}}
]}
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