deno on AWS Lambda

A deno runtime for AWS Lambda.

Deploy deno code via SAR application (see quick start), SAM, serverless, or bundle it yourself.

Define a handler function, for example:

// hello.ts

import {
  APIGatewayProxyEvent,
  APIGatewayProxyResult,
  Context
} from "https://deno.land/x/lambda/mod.ts";

export async function handler(
  event: APIGatewayProxyEvent,
  context: Context
): Promise<APIGatewayProxyResult> {
  return {
    body: `Welcome to deno ${Deno.version.deno} 🦕`,
    headers: { "content-type": "text/html;charset=utf8" },
    statusCode: 200
  };
}

Here the handler is hello.handler but this can be configured by the Handler setting.

Configuration

The following environment variables can be set to change deno-lambda's behavior:

HANDLER_EXT to set supported extension of handler file e.g. js or bundle.js (default ts).
DENO_CONFIG so deno runs with --config=$DENO_CONFIG.
DENO_DIR so deno runs with DENO_DIR=$DENO_DIR deno ....
DENO_IMPORTMAP so deno runs with --importmap=$DENO_IMPORTMAP.
DENO_LOCK so deno runs with --lock=$DENO_LOCK.
DENO_PREFIX prepends to console.log etc. a template literal, this can include requestId and level variables only (default ${level}\tRequestId: ${requestId}\r).

Further configuration TBD.

Types

deno-lambda exports Definitely Typed's aws-lambda types, listed in https://deno.land/x/lambda/mod.ts and defined in https://deno.land/x/lambda/types.d.ts.

It's good practice to reference the trigger's type in the handler, for example: APIGateway use APIGatewayProxyEvent and APIGatewayProxyResult, SQS use SQSEvent, etc.

Note: Despite there being multiple interfaces with the Context suffix, the second handler argument must be Context. These other interfaces can be accessed from the first argument (the event), for example event.requestContext of an APIGatewayProxyEvent.

How to deploy

The recommended way to deploy is to use the SAR application and either reference the outputted LayerArn as a layer in your function.

SAR application (see quick start)
SAM example
Serverless example (feat. Dynamodb)
Zipped source example, deno-lambda-example.zip, see bundling-code section.

See earlier version of quick start for a walkthrough of how to bundle yourself.

See the deno_dir-remapping section for how to include the correct DENO_DIR files to avoid any runtime compilation.

Warning

The way the lambda platform works means that promises not awaited in the handler may never be completed. This is because the underlying container can be suspended between invocations and will sometimes be shutdown afterwards.

export async function badHandler(
  event: APIGatewayProxyEvent,
  context: Context
): Promise<APIGatewayProxyResult> {
  somethingAsync(); // not awaited so may not complete
  return { statusCode: 200, body: "" };
}

export async function goodHandler(
  event: APIGatewayProxyEvent,
  context: Context
): Promise<APIGatewayProxyResult> {
  await somethingAsync();
  return { statusCode: 200, body: "" };
}

If you need to return immediately but want to invoke a longer running process you can async-invoke another lambda function (that does the await somethingAsync()).

Related projects

Bundling code

Create a zip file which contains:

an entry point which exports an async function (e.g. hello.ts)
include any other files needed to run the entry file
(optional but preferred) .deno_dir directory

*You can use a different directory with DENO_DIR environment variable.

Alternatively use deno bundle command and include the outputted js file, see also HANDLER_EXT.

DENO_DIR remapping

In order for compile artifacts to be recovered (and avoid runtime compilation) you must do the following directory remapping:

# Compile the handler (and cache dependencies and compile artifacts into DENO_DIR).
DENO_DIR=.deno_dir deno cache hello.ts

# This is the "remapping" step:
cp -R .deno_dir/gen/file/$PWD/ .deno_dir/LAMBDA_TASK_ROOT
# Note: We do the inverse of this operation in bootstrap.

zip lambda.zip -x '.deno_dir/gen/file/*' -r .deno_dir hello.ts  # other source files

Serverless pre-deploy remapping

In a serverless.yml this can be automatically prior to each upload using the serverless-scriptable-plugin:

plugins:
  - serverless-scriptable-plugin

custom:
  scriptHooks:
    before:package:createDeploymentArtifacts: DENO_DIR=.deno_dir deno cache api/candidate.ts && cp -R .deno_dir/gen/file/$PWD/ .deno_dir/LAMBDA_TASK_ROOT

See example-serverless/serverless.yml.

Advanced logging

You can set the way console.log etc. outputs to cloudwatch logs using DENO_PREFIX. You can include the line number using ${(new Error).stack.split('\n')[4]} or the datetime using ${new Date().toISOString()} (though the datetime of every cloudwatch event is part of the event itself.

Use these as a template literal, for example:

DENO_PREFIX=${level}\t${requestId}\t${(new Error).stack.split('\n')[4]}\r

This will prefix each log with the level, the request id and the line number:

Many thanks to Yoshiya Hinosawa's blogpost for the initial work on this runtime.

siokas / deno-lambda