Register Lambda Functions

You can either manually register AWS Lambda functions with Consul or use the Lambda registrator to automatically synchronize Lambda state into Consul.

To manually register AWS Lambda functions into Consul, you must register a service into Consul and then write a service defaults configuration entry for the Lambda.

The registrator automatically registers, reconfigures, and deregisters Lambdas based on the Lambda function's tags (refer to the AWS tag configuration documentation for details about tags).

We recommend using the Lambda registrator when possible so that you can keep the configuration entry up to date.

Requirements

• Consul 1.12.1 and later

Prerequisites

Complete the following prerequisites prior to registering your Lambda functions. You only need to perform these steps once.

Enable the Serverless Plugin

Add the following configuration to all Consul clients:

connect { enable_serverless_plugin = true, connect = true }

Refer to the enable_serverless_plugin configuration documentation for additional information.

Configure IAM Permissions for Envoy

The Envoy proxy that invokes Lambda must have the lambda:InvokeFunction AWS IAM permissions. In the following example, the IAM policy enables an IAM user or role to invoke the example Lambda function:

{
    "Version": "2012-10-17",
    "Statement": [
        {
            "Sid": "Invoke",
            "Effect": "Allow",
            "Action": [
                "lambda:InvokeFunction"
            ],
            "Resource": "arn:aws:lambda:us-east-1:123456789012:function:example"
        }
    ]
}

Define AWS IAM credentials in environment variables, EC2 metadata or ECS metadata. On AWS EKS, associate an IAM role with the proxy's ServiceAccount. Refer to the AWS IAM roles for service accounts documentation for instructions.

Optional: Set up a Terminating Gateway

If you intend to invoke Lambda services through a terminating gateway, the gateway must be registered and running in the Consul datacenter. Refer to the following documentation and tutorials for instructions on how to set up a terminating gateway:

• Terminating gateways documentation
• Terminating gateways on Kubernetes documentation
• Connect External Services to Consul With Terminating Gateways tutorial

To register a Lambda service with a terminating gateway, add the service to the Services field of the terminating gateway's terminating-gateway configuration entry.

Optional: Run a Mesh Gateway

You can set up a mesh gateway so that you can invoke Lambda services across datacenters and admin partitions. The mesh gateway must be running and registered in the relevant Consul datacenters and partitions. Refer to the following documentation and tutorials for instructions on how to set up mesh gateways:

• Mesh gateway documentation
• Connect Services Across Datacenters with Mesh Gateways tutorial
• Secure Service Mesh Communication Across Kubernetes Clusters tutorial

When using admin partitions, you must add Lambda services to the Services field of the exported-services configuration entry.

Automatic Lambda Function Registration

You can deploy the Lambda registrator to your environment to automatically register and deregister Lambda functions with Consul based on the function's tags. Refer to the AWS Lambda tags documentation to learn about tags.

The registrator runs as a Lambda function that is invoked by AWS EventBridge. Refer to the AWS EventBridge documentation for additional information.

EventBridge invokes the registrator using either AWS CloudTrail to syncronize with Consul in real-time or in scheduled intervals.

CloudTrail events typically synchronize updates, registration, and deregistration within one minute, but events may occasionally be delayed.

Scheduled events fully synchronize functions betwen Lambda and Consul to prevent entropy. By default, EventBridge triggers a full sync every five minutes.

The following diagram shows the flow of events from EventBridge into Consul:

1. EventBridge invokes the Lambda registrator based on CloudTrail Lambda events or a schedule.
2. Lambda registrator determines how to reconcile Lambda's control plane state with Consul state and ensures they are in sync by registering, updating, and deregistering Lambda services.

Deploy Lambda Registrator

1. Create a Terraform configuration and specify the lambda-registrator module. In the following example, the Lambda registrator is deployed to https://consul.example.com:8501. Refer to the Lambda registrator module documentation for additional usage information:

   module "lambda-registrator" {
       source  = "hashicorp/consul-lambda-registrator/aws//modules/lambda-registrator"
       name = "consul-lambda-registrator"
       consul_http_addr = "https://consul.example.com:8501"
       ca_cert_path = aws_ssm_parameter.ca-cert.name
       http_token_path = aws_ssm_parameter.acl-token.name
   }
   

2. Deploy Lambda registrator with terraform apply.

Optional: Store the CA Certificate in Parameter Store

When Lambda registrator makes a request to Consul's HTTP API over HTTPS and the Consul API is signed by a custom CA, Lambda registrator uses the CA certificate stored in AWS Parameter Store (refer to the Parameter Store documentation for additional information) to verify the authenticity of the Consul API. You can apply the following Terraform configuration to store Consul’s server CA in Parameter Store:

resource "aws_ssm_parameter" "ca-cert" {
  name        = "/lambda-registrator/ca-cert"
  type        = "SecureString"
  value       = <VALUE>
}

Optional: Store the ACL Token in Parameter Store

If Consul access control lists (ACLs) are enabled, Lambda registrator must present an ACL token stored in Parameter Store to access resources. You can use the Consul CLI, API, or the Terraform provider to facilitate the ACL workflow. The following procedure describes how to create and store a token from the command line:

1. Create an ACL policy that includes the following rule:

   rules.hcl

    service_prefix "" {
        policy = "write"
    }
   

2. Issue consul acl policy create command to create the policy. The following example creates a policy called lambda-registrator-policy containing permissions specified in rules.hcl:

    $ consul acl policy create -name "lambda-registrator-policy" -rules @rules.hcl
   

3. Issue the consul acl token create command to create the token. The following example creates a token linked to the lambda-registrator-policy policy:

    $ consul acl token create -policy-name "lambda-registrator-policy"
   

4. Store the token in Parameter Store by applying the following Terraform:

   resource "aws_ssm_parameter" "acl-token" {
       name        = "/lambda-registrator/acl-token"
       type        = "SecureString"
       value       = <VALUE>
    }
   

Lambda Registrator Configuration Options

Register Lambda Functions

Lambda registrator registers Lambda functions into Consul, regardless of how the functions are deployed. The following procedure describes how to register Lambda functions with the Lambda registrator using Terraform, but you can also deploy a Lambda function with CloudFormation, the AWS user interface, or Cloud Development Kit (CDK):

1. Add the aws_lambda_function resource to your Terraform configuration and specify the name of the Lambda function.
2. Add a tags block to the resource and specify the tags you want to use to register the function (refer to Supported Tags).

In the following example, the example Lambda function is registered using the enabled, payload-passthrough, and invocation-mode tags:

resource "aws_lambda_function" "example" {
  …
  function_name = "lambda"
  tags = {
    "serverless.consul.hashicorp.com/v1alpha1/lambda/enabled" = "true"
    "serverless.consul.hashicorp.com/alpha/lambda/payload-passthrough" = "true"
    "serverless.consul.hashicorp.com/alpha/lambda/invocation-mode" = "ASYNCHRONOUS"
  }
}

Supported Tags

The following tags are supported. In all cases, the <PREFIX> should be serverless.consul.hashicorp.com/v1alpha1/lambda. For example, serverless.consul.hashicorp.com/v1alpha1/lambda/enabled.

Manual Configuration

You can manually register Lambda functions if you are unable to automate the process using the Lambda registrator.

1. Create a configuration for registering the service. You can copy the following example and replace <SERVICE_NAME> with your Consul service name for the Lambda function:

   lambda.json

   {
     "Node": "lambdas",
     "SkipNodeUpdate": true,
     "NodeMeta": {
       "external-node": "true",
       "external-probe": "true"
     },
     "Service": {
       "Service": "<SERVICE_NAME>"
     }
   }
   

2. Save the configuration to lambda.json.

3. Send the configuration to the catalog/register API endpoint to register the service, for example:

   $ curl --request PUT --data @lambda.json localhost:8500/v1/catalog/register
   

4. Create the service-defaults configuration entry and include the AWS tags used to invoke the Lambda function in the Meta field (see Supported Meta Fields. The following example creates a service-defaults configuration entry named lambda:

   lambda-service-defaults.hcl

   Kind = "service-defaults"
   Name = "lambda"
   Protocol  = "http"
   Meta = {
     "serverless.consul.hashicorp.com/v1alpha1/lambda/enabled" = "true"
     "serverless.consul.hashicorp.com/v1alpha1/lambda/arn" = "<INSERT ARN HERE>"
     "serverless.consul.hashicorp.com/v1alpha1/lambda/payload-passthrough" = "true"
     "serverless.consul.hashicorp.com/v1alpha1/lambda/region" = "us-east-2"
   }
   

5. Issue the consul config write command to store the configuration entry. For example:

   $ consul config write lambda-service-defaults.hcl
   

Supported Meta Fields

The following tags are supported. In all cases, the <PREFIX> should be serverless.consul.hashicorp.com/v1alpha1/lambda. For example, serverless.consul.hashicorp.com/v1alpha1/lambda/enabled.