Temporal Auto-Scaled Workers

Automatically scale Temporal workers in response to workload. This project implements a Worker Controller Instance (WCI) — a long-running Temporal workflow that monitors task queue metrics and scales workers across cloud compute providers.

Overview

Each WCI manages a single deployment version (deployment name + build ID). It:

1. Receives task-add signals from the Temporal Matching Service
2. Periodically polls task queue backlog and dispatch metrics
3. Applies a configurable scaling algorithm to decide when to act
4. Invokes workers on the configured compute provider

Multiple scaling groups can be defined per WCI, each mapping a set of task queue types (workflow, activity, nexus) to a compute provider and scaling algorithm. One group can act as a catch-all for task types not claimed by other groups.

Supported Compute Providers

Provider	Type string	Launch strategy
AWS Lambda	aws-lambda	Invoke (one-off)
AWS ECS	aws-ecs	Worker set (managed scaling)
GCP Cloud Run	gcp-cloud-run	Worker set
Kubernetes	k8s	Worker set
Subprocess	subprocess	Invoke (dev/test only)

Invoke providers are called once per scaling event to start a short-lived worker. Worker-set providers manage a persistent pool whose size is adjusted up or down.

Supported Scaling Algorithms

Algorithm	Type string	Description
No-sync	no-sync	Scales up when backlog or arrival rate exceeds thresholds; cools down between invocations

Configuration

Dynamic config

Setting	Default	Description
WorkerControllerEnabled	false	Enable WCI per namespace
WorkerControllerMaxInstances	100	Max WCIs per namespace
WorkerControllerEnabledComputeProviders	all	Allowed compute provider types
WorkerControllerEnabledScalingAlgorithms	all	Allowed scaling algorithm types
WorkerControllerAWSIntermediaryRoles	[]	IAM role chain for AWS STS
WorkerControllerGCPIntermediaryServiceAccounts	[]	Service account chain for GCP
WorkerControllerAWSRequireRoleAndExternalID	true	Enforce role + external ID on AWS configs

Spec format

A WCI spec is a map of named scaling groups:

{
  "scaling_group_specs": {
    "workflows": {
      "task_types": ["WORKFLOW"],
      "compute": {
        "provider_type": "aws-lambda",
        "config": {
          "arn": "arn:aws:lambda:us-east-1:123456789012:function:my-worker",
          "role": "arn:aws:iam::123456789012:role/temporal-wci",
          "role_external_id": "my-external-id"
        }
      },
      "scaling": {
        "scaling_algorithm": "no-sync",
        "config": {
          "scale_up_backlog_threshold": "5",
          "scale_up_cooloff_ms": "500",
          "max_worker_lifetime_ms": "300000"
        }
      }
    },
    "activities": {
      "task_types": ["ACTIVITY", "NEXUS"],
      "compute": {
        "provider_type": "aws-ecs",
        "config": {
          "cluster": "my-cluster",
          "service": "my-worker-service",
          "region": "us-east-1",
          "role": "arn:aws:iam::123456789012:role/temporal-wci"
        }
      }
    }
  }
}

A group with no task_types acts as a catch-all for any task type not claimed by another group. At most one catch-all group is allowed.

no-sync algorithm config

Key	Default	Description
scale_up_backlog_threshold	0	Scale up when backlog exceeds this value
scale_up_cooloff_ms	100	Minimum milliseconds between scale-up actions
max_worker_lifetime_ms	600000	Re-invoke workers at least this often (10 min)
scale_up_dispatch_rate_epsilon	0	Suppress scale-up if dispatch rate is stable within this margin
metrics_poll_interval_ms	60000	How often to poll task queue metrics

Client API

import "go.temporal.io/auto-scaled-workers/wci/client"

// Register the Fx module in your server
fx.Provide(client.ClientProvider)

// Use the Client interface
type MyComponent struct {
    wciClient client.Client
}

// Create or update a WCI
err := wciClient.UpdateWorkerControllerInstance(ctx, ns, deploymentVersion, &client.UpdateWorkerControllerInstanceRequest{
    Spec: &client.Spec{
        ScalingGroupSpecs: map[string]client.ScalingGroupSpec{
            "default": {
                Compute: client.ComputeProviderSpec{
                    ProviderType: "aws-lambda",
                    Config:       map[string]string{"arn": "..."},
                },
            },
        },
    },
})

// List all WCIs
resp, err := wciClient.ListWorkerControllerInstances(ctx, ns, pageSize, nextPageToken)

// Delete a WCI
err := wciClient.DeleteWorkerControllerInstance(ctx, ns, deploymentVersion, conflictToken)

All mutating operations accept a ConflictToken for optimistic concurrency control. Obtain it from DescribeWorkerControllerInstance and pass it with updates to detect concurrent modifications.

Integration with Temporal Server

The TaskHookFactory returned by ClientProvider must be registered with the Temporal Matching Service. It intercepts task-add events and signals the appropriate WCI workflow.

Enable per namespace via the WorkerControllerEnabled dynamic config setting.

Building and running

# Build
make bins

# Run with SQLite (development)
make start

# Run tests
make test

The binary accepts a --config-file flag:

./temporal-auto-scaled-workers --config-file config/development-sqlite.yaml start

Scaling algorithm simulators

Interactive simulators for the scaling algorithms are available in docs/simulators/.

License

MIT