In containerised Frontends, Every environment requires rebuilding the same application just to change configuration like API URLs, feature flags, or auth endpoints.
Backend systems solved this problem long ago with runtime configuration. You build once and configure the application when it starts.
Static webapps never got a clean equivalent.
Most solutions today are ad-hoc:
- env.sh scripts that rewrite bundles
- CI pipelines rebuilding per environment
- templating HTML files
- framework-specific hacks
These approaches are fragile and tied to specific build tools.
I’ve been working on a small protocol called REP (Runtime Environment Protocol) that tries to solve this in a portable way.
The idea is simple:
1. Infrastructure provides configuration as environment variables.
2. A gateway injects them into the HTML response as a JSON payload.
3. The frontend reads them at runtime through a small SDK.
4. The payload is integrity-verified to prevent tampering.
example injected payload:
<script id="__rep__" type="application/json">
{
"public": {
"API_URL": "https://api.example.com"
},
"_meta": {
"integrity": "sha256-..."
}
}
</script>
The frontend can then read configuration at runtime instead of at build time.
This enables:
• build once, deploy anywhere
• environment configuration via infrastructure
• compatibility with static hosting and CDNs
• no rebuilds when configuration changes
The spec focuses on three things:
• a standard payload format
• secure integrity verification
• predictable injection semantics
I’m sharing it mostly to get feedback from people who deal with deploying frontend apps at scale.
Spec:
https://github.com/RuachTech/rep/blob/main/spec/REP-RFC-0001.md
URL: https://rep-protocol.dev
Curious if others have run into the same pain or solved this differently.
Backend systems solved this problem long ago with runtime configuration. You build once and configure the application when it starts.
Static webapps never got a clean equivalent.
Most solutions today are ad-hoc: - env.sh scripts that rewrite bundles - CI pipelines rebuilding per environment - templating HTML files - framework-specific hacks
These approaches are fragile and tied to specific build tools.
I’ve been working on a small protocol called REP (Runtime Environment Protocol) that tries to solve this in a portable way.
The idea is simple: 1. Infrastructure provides configuration as environment variables. 2. A gateway injects them into the HTML response as a JSON payload. 3. The frontend reads them at runtime through a small SDK. 4. The payload is integrity-verified to prevent tampering.
example injected payload: <script id="__rep__" type="application/json"> { "public": { "API_URL": "https://api.example.com" }, "_meta": { "integrity": "sha256-..." } } </script>
The frontend can then read configuration at runtime instead of at build time.
This enables: • build once, deploy anywhere • environment configuration via infrastructure • compatibility with static hosting and CDNs • no rebuilds when configuration changes
The spec focuses on three things: • a standard payload format • secure integrity verification • predictable injection semantics
I’m sharing it mostly to get feedback from people who deal with deploying frontend apps at scale.
Spec: https://github.com/RuachTech/rep/blob/main/spec/REP-RFC-0001.md
URL: https://rep-protocol.dev
Curious if others have run into the same pain or solved this differently.