server: implement decommission pre-check api

This change implements the `DecommissionPreCheck` RPC on the `Admin`
service, using the support for evaluating node decommission readiness by
checking each range introduced in cockroachdb#93758. In checking node decommission
readiness, only nodes that have a valid, non-`DECOMMISSIONED` liveness
status are checked, and ranges with replicas on the checked nodes that
encounter errors in attempting to allocate replacement replicas are
reported in the response. Ranges that have replicas on multiple checked
nodes have their errors reported for each nodeID in the request list.

Depends on cockroachdb#93758, cockroachdb#90222.

Epic: CRDB-20924

Release note: None

pkg/server/admin.go

@@ -2648,7 +2648,88 @@ func (s *adminServer) getStatementBundle(ctx context.Context, id int64, w http.R
 func (s *systemAdminServer) DecommissionPreCheck(
 	ctx context.Context, req *serverpb.DecommissionPreCheckRequest,
 ) (*serverpb.DecommissionPreCheckResponse, error) {
-	return nil, grpcstatus.Errorf(codes.Unimplemented, "method DecommissionPreCheck not implemented")
+	var collectTraces bool
+	if s := tracing.SpanFromContext(ctx); (s != nil && s.RecordingType() != tracingpb.RecordingOff) || req.CollectTraces {
+		collectTraces = true
+	}
+
+	// Initially evaluate node liveness status, so we filter the nodes to check.
+	var nodesToCheck []roachpb.NodeID
+	livenessStatusByNodeID, err := getLivenessStatusMap(ctx, s.nodeLiveness, s.clock.Now().GoTime(), s.st)
+	if err != nil {
+		return nil, serverError(ctx, err)
+	}
+
+	resp := &serverpb.DecommissionPreCheckResponse{}
+
+	// Any nodes that are already decommissioned or have unknown liveness should
+	// not be checked, and are added to response without replica counts or errors.
+	for _, nID := range req.NodeIDs {
+		livenessStatus := livenessStatusByNodeID[nID]
+		if livenessStatus == livenesspb.NodeLivenessStatus_UNKNOWN {
+			resp.CheckedNodes = append(resp.CheckedNodes, serverpb.DecommissionPreCheckResponse_NodeCheckResult{
+				NodeID:                nID,
+				DecommissionReadiness: serverpb.DecommissionPreCheckResponse_UNKNOWN,
+				LivenessStatus:        livenessStatus,
+			})
+		} else if livenessStatus == livenesspb.NodeLivenessStatus_DECOMMISSIONED {
+			resp.CheckedNodes = append(resp.CheckedNodes, serverpb.DecommissionPreCheckResponse_NodeCheckResult{
+				NodeID:                nID,
+				DecommissionReadiness: serverpb.DecommissionPreCheckResponse_ALREADY_DECOMMISSIONED,
+				LivenessStatus:        livenessStatus,
+			})
+		} else {
+			nodesToCheck = append(nodesToCheck, nID)
+		}
+	}
+
+	results, err := s.server.DecommissionPreCheck(ctx, nodesToCheck, req.StrictReadiness, collectTraces, int(req.NumReplicaReport))
+	if err != nil {
+		return nil, err
+	}
+
+	// Collect ranges that encountered errors by the nodes on which their replicas
+	// exist. Ranges with replicas on multiple checked nodes will result in the
+	// error being reported for each nodeID.
+	rangeCheckErrsByNode := make(map[roachpb.NodeID][]serverpb.DecommissionPreCheckResponse_RangeCheckResult)
+	for _, rangeWithErr := range results.rangesNotReady {
+		rangeCheckResult := serverpb.DecommissionPreCheckResponse_RangeCheckResult{
+			RangeID: rangeWithErr.desc.RangeID,
+			Action:  rangeWithErr.action,
+			Events:  recordedSpansToTraceEvents(rangeWithErr.tracingSpans),
+			Error:   rangeWithErr.err.Error(),
+		}
+
+		for _, nID := range nodesToCheck {
+			if rangeWithErr.desc.Replicas().HasReplicaOnNode(nID) {
+				rangeCheckErrsByNode[nID] = append(rangeCheckErrsByNode[nID], rangeCheckResult)
+			}
+		}
+	}
+
+	// Evaluate readiness for each node to check based on how many ranges have
+	// replicas on the node that did not pass checks.
+	for _, nID := range nodesToCheck {
+		numReplicas := len(results.replicasByNode[nID])
+		var readiness serverpb.DecommissionPreCheckResponse_NodeReadiness
+		if len(rangeCheckErrsByNode[nID]) > 0 {
+			readiness = serverpb.DecommissionPreCheckResponse_ALLOCATION_ERRORS
+		} else {
+			readiness = serverpb.DecommissionPreCheckResponse_READY
+		}
+
+		nodeCheckResult := serverpb.DecommissionPreCheckResponse_NodeCheckResult{
+			NodeID:                nID,
+			DecommissionReadiness: readiness,
+			LivenessStatus:        livenessStatusByNodeID[nID],
+			ReplicaCount:          int64(numReplicas),
+			CheckedRanges:         rangeCheckErrsByNode[nID],
+		}
+
+		resp.CheckedNodes = append(resp.CheckedNodes, nodeCheckResult)
+	}
+
+	return resp, nil
 }
 
 // DecommissionStatus returns the DecommissionStatus for all or the given nodes.