# Serverless Workers on AWS Lambda - Go SDK

> Write a Temporal Worker that runs on AWS Lambda using the Go SDK lambdaworker package.

> **Pre-release**
> To request access during Pre-release, create a [support ticket](/cloud/support#support-ticket) or contact your account team.
> APIs are experimental and may be subject to backwards-incompatible changes.
> [Sign up for updates](https://temporal.io/pages/serverless-workers-updates) to be notified when Serverless Workers reach Public Preview.

The `lambdaworker` package lets you run a Temporal Serverless Worker on AWS Lambda.
Deploy your Worker code as a Lambda function, and Temporal Cloud invokes it when Tasks arrive.
Each invocation starts a Worker, polls for Tasks, then gracefully shuts down before a configurable invocation deadline.
You register Workflows and Activities the same way you would with a standard Worker.

For a full end-to-end deployment guide covering AWS IAM setup, compute configuration, and verification, see [Deploy a Serverless Worker](/production-deployment/worker-deployments/serverless-workers).

## Create and run a Worker in Lambda 

Use the `RunWorker` function to start a Lambda-based Worker.
Pass a `WorkerDeploymentVersion` and a callback that registers your Workflows and Activities.

<!--SNIPSTART go-lambda-worker {"selectedLines": ["1-6", "8-18", "22-30"]}-->
[lambda-worker/worker/main.go](https://github.com/temporalio/samples-go/blob/main/lambda-worker/worker/main.go)
```go
package main

import (
	greeting "github.com/temporalio/samples-go/lambda-worker/greeting"

	lambdaworker "go.temporal.io/sdk/contrib/aws/lambdaworker"
// ...
	"go.temporal.io/sdk/worker"
	"go.temporal.io/sdk/workflow"
)

func main() {
	lambdaworker.RunWorker(worker.WorkerDeploymentVersion{
		DeploymentName: "my-app",
		BuildID:        "build-1",
	}, func(opts *lambdaworker.Options) error {
		opts.TaskQueue = "serverless-task-queue-1"

// ...

		opts.RegisterWorkflowWithOptions(greeting.SampleWorkflow, workflow.RegisterOptions{
			VersioningBehavior: workflow.VersioningBehaviorPinned,
		})
		opts.RegisterActivity(greeting.HelloActivity)

		return nil
	})
}
```
<!--SNIPEND-->

The `WorkerDeploymentVersion` is required.
Worker Deployment Versioning is always enabled for Serverless Workers.
Each Workflow must have a [versioning behavior](/worker-versioning#versioning-behaviors), either `AutoUpgrade` or `Pinned`.
Set it per-Workflow at registration time, or set a worker-level default with `DefaultVersioningBehavior` in `DeploymentOptions`.

The `Options` callback gives you access to the same registration methods you use with a traditional Worker: `RegisterWorkflow`, `RegisterWorkflowWithOptions`, `RegisterActivity`, `RegisterActivityWithOptions`, and `RegisterNexusService`.

## Configure the Temporal connection 

The `lambdaworker` package automatically loads Temporal client configuration from a TOML config file and environment variables. Refer to [Environment Configuration](/develop/environment-configuration) for more details.

The config file is resolved in order:

1. `TEMPORAL_CONFIG_FILE` environment variable, if set.
2. `temporal.toml` in `$LAMBDA_TASK_ROOT` (typically `/var/task`).
3. `temporal.toml` in the current working directory.

The file is optional. If absent, only environment variables are used.

Encrypt sensitive values like TLS keys or API keys. Refer to [AWS documentation](https://docs.aws.amazon.com/lambda/latest/dg/configuration-envvars-encryption.html) for options.

## Adjust Worker defaults for Lambda 

The `lambdaworker` package applies conservative defaults suited to short-lived Lambda invocations.
These differ from standard Worker defaults to avoid overcommitting resources in a constrained environment.
Except for `ShutdownDeadlineBuffer`, these are the same [`worker.Options`](https://pkg.go.dev/go.temporal.io/sdk@v1.42.0/internal#WorkerOptions) available to any Temporal Worker, just with lower values for Lambda's constrained environment.

| Setting | Lambda default |
|---|---|
| `MaxConcurrentActivityExecutionSize` | 2 |
| `MaxConcurrentWorkflowTaskExecutionSize` | 10 |
| `MaxConcurrentLocalActivityExecutionSize` | 2 |
| `MaxConcurrentNexusTaskExecutionSize` | 5 |
| `MaxConcurrentActivityTaskPollers` | 1 |
| `MaxConcurrentWorkflowTaskPollers` | 2 |
| `MaxConcurrentNexusTaskPollers` | 1 |
| `WorkerStopTimeout` | 5 seconds |
| `DisableEagerActivities` | Always true |
| Sticky cache size | 100 |
| `ShutdownDeadlineBuffer` | 7 seconds |

`DisableEagerActivities` is always true and cannot be overridden.
Eager Activities require a persistent connection, which Lambda invocations don't maintain.

`ShutdownDeadlineBuffer` is specific to the `lambdaworker` package.
It controls how much time before the Lambda deadline the Worker begins its graceful shutdown.
The default is `WorkerStopTimeout` + 2 seconds.

If your Worker handles long-running Activities, increase `WorkerStopTimeout`, `ShutdownDeadlineBuffer`, and the Lambda invocation deadline (`--timeout`) together.
For guidance on how these values relate, see [Tuning for long-running Activities](/serverless-workers#tuning-for-long-running-activities).

## Add observability with OpenTelemetry 

The `lambdaworker/otel` sub-package provides OpenTelemetry integration with defaults configured for the [AWS Distro for OpenTelemetry (ADOT)](https://aws-otel.github.io/docs/getting-started/lambda) Lambda layer.
With this enabled, the Worker emits SDK metrics and distributed traces for Workflow and Activity executions.
The ADOT Lambda layer collects this telemetry and can forward traces to AWS X-Ray and metrics to Amazon CloudWatch.

The underlying metrics and traces are the same ones the Go SDK emits in any environment.
For general observability concepts and the full list of available metrics, see [Observability - Go SDK](/develop/go/platform/observability) and the [SDK metrics reference](/references/sdk-metrics).

<!--SNIPSTART go-lambda-worker-->
[lambda-worker/worker/main.go](https://github.com/temporalio/samples-go/blob/main/lambda-worker/worker/main.go)
```go
package main

import (
	greeting "github.com/temporalio/samples-go/lambda-worker/greeting"

	lambdaworker "go.temporal.io/sdk/contrib/aws/lambdaworker"
	otel "go.temporal.io/sdk/contrib/aws/lambdaworker/otel"
	"go.temporal.io/sdk/worker"
	"go.temporal.io/sdk/workflow"
)

func main() {
	lambdaworker.RunWorker(worker.WorkerDeploymentVersion{
		DeploymentName: "my-app",
		BuildID:        "build-1",
	}, func(opts *lambdaworker.Options) error {
		opts.TaskQueue = "serverless-task-queue-1"

		if err := otel.ApplyDefaults(opts, &opts.ClientOptions, otel.Options{}); err != nil {
			return err
		}

		opts.RegisterWorkflowWithOptions(greeting.SampleWorkflow, workflow.RegisterOptions{
			VersioningBehavior: workflow.VersioningBehaviorPinned,
		})
		opts.RegisterActivity(greeting.HelloActivity)

		return nil
	})
}
```
<!--SNIPEND-->

`ApplyDefaults` configures both metrics and tracing.
By default, telemetry is sent to `localhost:4317`, which is the ADOT Lambda layer's default collector endpoint.

To collect this telemetry, attach the [ADOT Collector layer](https://aws-otel.github.io/docs/getting-started/lambda) to your Lambda function.
The layer runs a collector sidecar that receives telemetry on `localhost:4317` and forwards traces to X-Ray and metrics to CloudWatch.
Go does not need a language-specific ADOT layer because the OTel SDK is compiled into the binary.

The default Collector configuration does not route OpenTelemetry Protocol (OTLP) data to the traces pipeline.
You must provide a custom Collector configuration that wires the OTLP receiver to both the traces and metrics pipelines.
Bundle the following `otel-collector-config.yaml` in your Lambda deployment package:

<!--SNIPSTART go-lambda-worker-otel-collector-config-->
[lambda-worker/otel-collector-config.yaml](https://github.com/temporalio/samples-go/blob/main/lambda-worker/otel-collector-config.yaml)
```yaml
receivers:
    otlp:
        protocols:
            grpc:
                endpoint: "localhost:4317"
            http:
                endpoint: "localhost:4318"

exporters:
    debug:
    awsxray:
        region: us-west-2
    awsemf:
        # AWS EMF exporter for metrics
        # These are example configurations
        namespace: TemporalWorkerMetrics
        log_group_name: /aws/lambda/<your-function-name>
        region: us-west-2
        dimension_rollup_option: NoDimensionRollup
        resource_to_telemetry_conversion:
            enabled: true

service:
    pipelines:
        traces:
            receivers: [otlp]
            exporters: [awsxray, debug]
        metrics:
            receivers: [otlp]
            exporters: [awsemf]
    telemetry:
        logs:
            level: debug
        metrics:
            address: localhost:8888
```
<!--SNIPEND-->

Set the following environment variable on the Lambda function to point the Collector at the bundled config:

- `OPENTELEMETRY_COLLECTOR_CONFIG_URI=/var/task/otel-collector-config.yaml`

Enable X-Ray active tracing on the Lambda function:

```bash
aws lambda update-function-configuration \
  --function-name <your-function-name> \
  --tracing-config Mode=Active
```

The Lambda execution role must have permissions to write to X-Ray and CloudWatch.
Add `xray:PutTraceSegments`, `xray:PutTelemetryRecords`, and `cloudwatch:PutMetricData` permissions to the execution role.
Without these permissions, the Collector fails silently and no telemetry appears.

If you only need metrics or tracing, use `otel.ApplyMetrics` or `otel.ApplyTracing` individually.