Custom runtime for lambda - example in main.zig
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lambda-zig: A Custom Runtime for AWS Lambda

This is a sample custom runtime built in zig (0.11). Simple projects will execute in <1ms, with a cold start init time of approximately 11ms.

Some custom build steps have been added to build.zig, which will only currently appear if compiling from a linux operating system:

  • zig build iam: Deploy and record a default IAM role for the lambda function
  • zig build package: Package the lambda function for upload
  • zig build deploy: Deploy the lambda function
  • zig build remoterun: Run the lambda function

Custom options:

  • function-name: set the name of the AWS Lambda function
  • payload: Use this to set the payload of the function when run using zig build remoterun

Additionally, a custom IAM role can be used for the function by appending -- --role myawesomerole to the zig build deploy command. This has not really been tested. The role name is cached in zig-out/bin/iam_role_name, so you can also just set that to the full arn of your iam role if you'd like.

The AWS Lambda function is compiled as a linux ARM64 executable. Since the build.zig calls out to the shell for AWS operations, you will need the AWS CLI. v2.2.43 has been tested.


  • Unhandled invocation errors seem to be causing timeouts
  • zig build options only appear if compiling using linux, although it should be trivial to make it work on other Unix-like operating systems (e.g. macos, freebsd). In fact, it will likely work with just a change to the operating system check
  • There are a ton of TODO's in this code. Current state is more of a proof of concept. PRs are welcome!

A sample project using this runtime can be found at

Using the zig package manager

The zig package manager works just fine in build.zig, which works well for use of this runtime.

To add lambda package/deployment steps to another project:

  1. zig build init-exe
  2. Add a build.zig.zon similar to the below
  3. Add a line to build.zig to add necessary build options, etc. Not the build function return type should be changed from void to !void


try @import("lambda-zig").lambdaBuildOptions(b, exe);


    .name = "lambda-zig",
    .version = "0.1.0",
    .dependencies = .{
        .@"lambda-zig" = .{
            .url = "",
            .hash = "122037c357f834ffddf7b3a514f55edd5a4d7a3cde138a4021b6ac51be8fd2926000",

That's it! Now you should have the 4 custom build steps