nomad/contributing/checklist-rpc-endpoint.md

New/Updated RPC Endpoint Checklist

Prefer adding a new message to changing any existing RPC messages.

Code

• Request struct and *RequestType constant in nomad/structs/structs.go. Append the constant, old constant values must remain unchanged. Just add the request type to this file, all other resource definitions must be on their own separate file.

• In nomad/fsm.go, add a dispatch case to the switch statement in (n *nomadFSM) Apply

  • *nomadFSM method to decode the request and call the state method

• State method for modifying objects in a Txn in the state package, located in nomad/state/. Every new resource should have its own file and test file, named using the convention nomad/state/state_store_[resource].go and nomad/state/state_store_[resource]_test.go

• Handler for the request in nomad/foo_endpoint.go

  • RPCs are resolved by matching the method name for bound structs net/rpc
  • Register any new RPC structs in nomad/server.go
  • Authentication:
    • For RPCs that support HTTP APIs, call Authenticate before forwarding. Return any error after frowarding, and call ResolveACL to get an ACL to check.
    • For RPCs that support client-to-server RPCs only, use AuthenticateClientOnly before forwarding. Check the AllowClientOp ACL after forwarding.
    • For RPCs that support server-to-server RPCs only, use AuthenticateServerOnly before forwarding. Check the AllowServerOp ACL before forwarding.
  • Authorization:
    • Use ResolveACL to turn the authenticated request into an ACL to check.
    • For Update/Get/Delete RPCs, check ACLs before hitting the state store.
    • For List RPCs, use ACLs as a filter on the query.
    • Never check that the ACL object is nil to bypass authorization. The authorization methods in acl/acl.go should already handle nil ACL objects correctly (by rejecting them).

• Wrapper for the HTTP request in command/agent/foo_endpoint.go

  • Backwards compatibility requires a new endpoint, an upgraded client or server may be forwarding this request to an old server, without support for the new RPC
  • RPCs triggered by an internal process may not need support
  • Check ACLs as an optimization

• nomad/core_sched.go sends many RPCs

  • ServersMeetMinimumVersion asserts that the server cluster is upgraded, so use this to guard sending the new RPC, else send the old RPC
  • Version must match the actual release version!

• If implementing a Client RPC...

  • Use QueryOptions instead of WriteRequest in the Request struct as WriteRequest is only for Raft writes.
  • Set QueryOptions.AllowStale = true in the Server RPC forwarder to avoid an infinite loop between leaders and followers when a Client RPC is forwarded through a follower. See https://github.com/hashicorp/nomad/issues/16517

Docs

• Changelog
• Metrics
• API docs for RPCs with an HTTP endpoint, include ACLs, params, and example response body.