Nexus Operations

Cross-namespace durable communication using Temporal Nexus (GA).

Overview

Nexus enables workflows in separate namespaces to call each other through typed service contracts with Temporal's full durable execution guarantees.

Feature	Nexus	Child Workflows	Activities	Signals
Cross-namespace	Yes	No (same NS only)	No	No
Durable execution	Yes	Yes	No	N/A
Request-response	Yes	Yes	Yes	No (one-way)
Arbitrary duration	Yes	Yes	No (< 10s)	N/A
Loose coupling	Yes	No	Yes	N/A
Service contract	Typed interface	Parent-child	Implicit	N/A

Architecture:

┌──────────────────┐   Nexus Endpoint   ┌──────────────────┐
│  Caller Namespace │──────────────────>│ Handler Namespace │
│  ┌──────────────┐│   (routes to       │┌────────────────┐│
│  │Caller Workflow││   target NS +     ││Handler Worker   ││
│  │  NexusClient  ││   task queue)     ││ NexusService    ││
│  └──────────────┘│                    │└────────────────┘│
└──────────────────┘                    └──────────────────┘

When to Use Nexus

Use Nexus when:

• Teams maintain separate namespaces and need to call each other's workflows
• You need durable execution guarantees across namespace boundaries
• You want clean, typed service contracts between teams/services
• You need both synchronous (< 10s) and asynchronous (long-running) cross-namespace calls

Don't use Nexus when:

• All workflows live in one namespace — use child workflows instead
• You need simple fire-and-forget notifications — use signals
• You need quick external API calls from workflows — use activities
• You need synchronous state mutation on a running workflow — use updates
• The added complexity (endpoints, handler workers, service contracts) isn't justified by the isolation benefits

Choosing the Right Pattern

Requirement	Best Option
Same namespace, simple decomposition	Child Workflows
External side effects, no durability needed	Activities
One-way notification to running workflow	Signals
Synchronous state mutation	Updates
Cross-namespace, durable, request-response	Nexus
Cross-namespace, short request (< 10s)	Nexus sync operation
Cross-namespace, long-running process	Nexus async operation

SDK Support

SDK	Status	Notes
Go	GA	Full production support
Java	GA	Full production support (1.28.0+)
Python	Public Preview	Recommended for production, API may improve
TypeScript	Experimental	APIs may have breaking changes
.NET	Experimental	APIs may have breaking changes (1.9.0+)

Key Concepts

Nexus Endpoint: A cluster-level routing resource that maps a name to a target namespace + task queue. Decouples callers from handler location. Created via CLI or Terraform.

Nexus Service: A named collection of Nexus Operations. Defines the microservice contract. Registered on handler workers.

Nexus Operation: An arbitrary-duration operation — either:

• Synchronous: RPC-style, completes immediately (< 10s), handler returns result directly
• Asynchronous: Starts a workflow as the backing operation, returns an operation token for tracking

Nexus Machinery: Temporal's built-in infrastructure providing at-least-once execution, automatic retries, circuit breaking, and rate limiting for Nexus calls.

Endpoint Setup

Prerequisites: caller and handler namespaces must exist.

# Create namespaces (if not already present)
temporal operator namespace create --namespace handler-ns
temporal operator namespace create --namespace caller-ns

# Create Nexus endpoint
temporal operator nexus endpoint create \
  --name my-endpoint \
  --target-namespace handler-ns \
  --target-task-queue handler-tq

# List endpoints
temporal operator nexus endpoint list

# Describe endpoint
temporal operator nexus endpoint describe --name my-endpoint

# Update endpoint
temporal operator nexus endpoint update \
  --name my-endpoint \
  --target-task-queue new-handler-tq

# Delete endpoint
temporal operator nexus endpoint delete --name my-endpoint

Handler Implementation (Go SDK)

Synchronous Operation

For requests completing in < 10 seconds:

import (
    "context"
    "github.com/nexus-rpc/sdk-go/nexus"
)

// Synchronous operation — returns result directly
var EchoOp = nexus.NewSyncOperation("echo",
    func(ctx context.Context, input EchoInput, opts nexus.StartOperationOptions) (EchoOutput, error) {
        return EchoOutput{Message: input.Message}, nil
    })

Asynchronous (Workflow-Backed) Operation

For long-running processes:

import (
    "context"
    "go.temporal.io/sdk/client"
    temporalnexus "go.temporal.io/sdk/temporalnexus"
)

// Async operation — starts a workflow, returns when workflow completes
var ProcessOrderOp = temporalnexus.NewWorkflowRunOperation("process-order",
    ProcessOrderWorkflow,
    func(ctx context.Context, input OrderInput, opts nexus.StartOperationOptions) (client.StartWorkflowOptions, error) {
        return client.StartWorkflowOptions{
            // Use RequestID as workflow ID to deduplicate retries
            ID: opts.RequestID,
        }, nil
    })

Service Definition and Worker Registration

import (
    "github.com/nexus-rpc/sdk-go/nexus"
    "go.temporal.io/sdk/worker"
)

// Create and register service
func registerNexusService(w worker.Worker) {
    service := nexus.NewService("order-service")
    service.Register(EchoOp)
    service.Register(ProcessOrderOp)
    w.RegisterNexusService(service)
}

Other SDK Implementations

For TypeScript (experimental), Python (public preview), and Java (GA) handler and caller examples, see references/nexus-multi-sdk.md.

Caller Workflow Patterns (Go SDK)

func CallerWorkflow(ctx workflow.Context, input CallerInput) (*CallerOutput, error) {
    // Create Nexus client — endpoint name + service name
    nexusClient := workflow.NewNexusClient("my-endpoint", "order-service")

    // Execute operation (blocks until result)
    future := nexusClient.ExecuteOperation(ctx, ProcessOrderOp, OrderInput{
        ID: input.OrderID,
    }, workflow.NexusOperationOptions{
        ScheduleToCloseTimeout: 10 * time.Minute,
    })

    var result OrderOutput
    if err := future.Get(ctx, &result); err != nil {
        return nil, fmt.Errorf("nexus operation failed: %w", err)
    }

    return &CallerOutput{OrderResult: result}, nil
}

Error Handling

Error Types

Error Type	Where	Description	Retryable?
OperationError	Handler	Application-level failure	No
HandlerError	Handler	Framework/infrastructure error	Depends on type
NexusOperationFailure	Caller	Wraps handler error for caller workflow	No

Handling Errors in Callers (Go)

var result OrderOutput
if err := future.Get(ctx, &result); err != nil {
    var nexusErr *temporal.NexusOperationFailure
    if errors.As(err, &nexusErr) {
        // Application-level failure from handler
        logger.Error("Nexus operation failed", "error", nexusErr)
        return nil, err
    }
    // Other errors (timeout, cancellation)
    return nil, err
}

Returning Errors from Handlers (Go)

var ProcessOp = nexus.NewSyncOperation("process",
    func(ctx context.Context, input Input, opts nexus.StartOperationOptions) (Output, error) {
        if input.ID == "" {
            // Return application error — caller gets NexusOperationFailure
            return Output{}, nexus.HandlerErrorf(nexus.HandlerErrorTypeBadRequest, "ID is required")
        }
        return Output{Result: "ok"}, nil
    })

Event History

Nexus-specific events in caller workflow history:

Event	Meaning
NexusOperationScheduled	Caller scheduled a Nexus operation
NexusOperationStarted	Async operation accepted by handler (returned operation token)
NexusOperationCompleted	Operation finished successfully
NexusOperationFailed	Operation returned an error
NexusOperationCanceled	Operation was canceled
NexusOperationTimedOut	scheduleToCloseTimeout exceeded

Best Practices

• Use sync operations for < 10s requests — simpler, lower overhead
• Use async (workflow-backed) for long-running work — gets full workflow durability
• Deduplicate with RequestID — use opts.RequestID as workflow ID in async handlers to safely handle retries
• Implement idempotent handlers — Nexus provides at-least-once semantics, so handlers may be called more than once
• Always set scheduleToCloseTimeout on caller side — without it, operations may hang indefinitely
• Treat Nexus service contracts as stable APIs — they're microservice boundaries; version them carefully
• Use separate namespaces for caller and handler to get true isolation benefits
• Don't use Nexus within a single namespace — child workflows are simpler and equally durable

Additional Resources

Reference Files

For detailed patterns, consult:

• references/nexus-patterns.md - Advanced Nexus usage patterns
• references/nexus-multi-sdk.md - Multi-SDK implementation examples