Go, Wasm, & Bazel: A Blueprint for Hermetic, High-Performance Web Applications

11th November 2025

Agenda

• What is WebAssembly
• Go and WebAssembly
• Challenges with Go and WebAssembly
• Solution with Bazel
• Advantages of Bazel builds over go build
• Migration path from go build to Bazel
• Future of Go and WebAssembly with Bazel
• References

Speaker - Rajiv Ranjan Singh

x.com/therajiv

• Software Engineer (JL3) at A.P. Moller Maersk
• Graduated from JSSATE, Bengaluru, India
• GSoC 2022, LFX Mentorship 2021, and GSoD 2020 & 2021
• Mentored in GSoC 2023, 2024, and 2025 with Jenkins
• Previously worked with Lummo, redBus, and Economize

Speaker - Naman Lakhwani

x.com/lakhwani_jii

• Software Developer at Allen Digital
• Previously with VMware, HackerRank, and Nirmata
• Kubernetes v1.26 and v1.30 release shadow
• Google Summer of Code and Linux Foundation mentee
• Graduate of IIIT Gwalior

What is WebAssembly?

• WebAssembly is a binary instruction format
• Compact bytecode used as a compilation target
• Virtual machines compile and execute at runtime
• Host functions enable external communication
• //go:wasmimport and //go:wasmexport are used for function calls

Go and WebAssembly

• WebAssembly support introduced in Go 1.11 (2018)
• WASI preview 1 target added in Go 1.21 (2023)
• Ongoing work toward WASI preview 2 and improved module support

Challenges with Go and WebAssembly

• Non-hermetic builds lead to inconsistent results across environments
• Complex dependency management and caching for large Go projects
• Limited reproducibility when compiling Go to Wasm
• Slow incremental rebuilds and lack of parallel execution
• Difficult integration with CI and CD pipelines for WebAssembly builds

Solution with Bazel

• Hermetic, sandboxed builds guarantee fully reproducible Wasm artifacts
• Intelligent and shareable caching drastically speeds up builds through remote caches
• True reproducibility ensures byte-for-byte identical Wasm binaries
• Fine-grained parallel execution rebuilds only what is necessary, in parallel
• Reliable CI and CD integration creates a single, fast, and consistent build pipeline

Advantages of Bazel Builds over go build

• Hermetic and reproducible builds
• Advanced and shareable caching
• Fine-grained parallelism
• Polyglot build integration

Migration from go build to Bazel

Three files to create:

1. MODULE.bazel - Downloads exact Go version
2. BUILD.bazel - Defines build targets
3. main.go - Your Go code (unchanged)

Keep: Your existing go.mod file

Migration from go build to Bazel

1. MODULE.bazel

module(
    name = "bazelcon-2025",
    version = "1.0.0",
)

# Bazel dependencies
bazel_dep(name = "rules_go", version = "0.50.1")
bazel_dep(name = "gazelle", version = "0.39.1")

# Go SDK setup
go_sdk = use_extension("@rules_go//go:extensions.bzl", "go_sdk")
go_sdk.download(version = "1.23.4")

# Go dependencies
go_deps = use_extension("@gazelle//:extensions.bzl", "go_deps")
go_deps.from_file(go_mod = "//:go.mod")
use_repo(go_deps)

Migration from go build to Bazel

2. BUILD.bazel

Migration from go build to Bazel

3. main.go

package main

import (
    "fmt"
    "runtime"
)

func main() {
    fmt.Println("Hello, Bazel, WASM, and Go!")
    fmt.Printf("GOOS: %s, GOARCH: %s\n", runtime.GOOS, runtime.GOARCH)
}

Step 4: Build and Run

Build:

bazel build //:app
bazel build //:app-wasm

Run native:

$ ./bazel-bin/app_/app
Hello, Bazel, WASM, and Go!
GOOS: darwin, GOARCH: arm64

Run WASM:

$ wasmtime ./bazel-bin/app-wasm_/app-wasm
Hello, Bazel, WASM, and Go!
GOOS: wasip1, GOARCH: wasm

Future of Go and WebAssembly with Bazel

• go:wasmexport Allows declaring exported functions in Wasm modules
• GOARCH=wasm32 Defines a 32-bit WebAssembly architecture for Go
• WASI Preview 2 (GOOS=wasip2) Introduces the next generation of WASI APIs
• Bazel Integration Enables reproducible and hermetic builds for Go to Wasm workflows

References

• https://go.dev/wiki/WebAssembly
• https://webassembly.org
• https://bazelcon-2025.fly.dev
• https://github.com/iamrajiv/bazelcon-2025

Thank you