Federated collections¶

• Fetch collection record by uuid
  • use federated record retrieval strategy, already developed.
• Fetch collection record by PDH
  • No location hint. Must send out request to all federated clusters.
  • Read-only, only need to support GET operation
• Can cache result by PDH.

Record will have a manifest with signed blocks. However these blocks will be signed for the origin cluster.

Client needs to be able to fetch blocks from remote cluster.

arvados-controller could add block hints, using existing feature in the Python and Go SDK:

• Blocks in a manifest can include a hint in the form "+K@zzzzz". Python SDK will attempt to fetch the block from "https://keep.zzzzz.arvadosapi.com/"
  • Must conform to a particular naming DNS scheme.
  • Could be generalized by looking up in "remote_hosts" and using the "keep_services.accessible" API.
  • Every block will be requested from remote every time, because client is contacting remote server directly, limited opportunity for edge caching.

• Hint can also be a uuid of a "local gateway service". This is instructs client to use a specific service from the keep_services table (indicated as "service_type" of "gateway:")
  • Direct requests through a specific service
  • Does not encode which remote cluster to pull a block from.
  • Gateway service could search for blocks by sending request to every federated cluster
  • Gateway service can cache blocks so they don't need to be re-fetched from remote.