Go on Previewops

Previewops builds whatever your Dockerfile produces and runs it as a container, so Go needs no special support. What it does need is what every stack needs: read the injected PORT and listen on 0.0.0.0.


Read the port	`os.Getenv("PORT")`
Bind all interfaces	`http.ListenAndServe(":"+port, nil)`

Dockerfile

FROM golang:1.23-alpine AS build
WORKDIR /src
COPY . .
RUN go build -o /out/server ./cmd/server

FROM alpine:3.20
COPY --from=build /out/server /server
ENV PORT=8080
CMD ["/server"]

ENV PORT=8080 is only a default. Previewops overrides it at deploy time, so the app must read the value rather than assume it.

Application code

A typical setup with net/http:

package main

import (
    "log"
    "net/http"
    "os"
)

func main() {
    port := os.Getenv("PORT")
    if port == "" {
        port = "8080"
    }

    http.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
        w.Write([]byte("ok"))
    })

    // ":"+port binds every interface. "localhost:"+port would not.
    log.Fatal(http.ListenAndServe(":"+port, nil))
}

Go-specific pitfalls

localhost:8080 binds loopback only. Use ":"+port with no host so the listener accepts proxied connections.
CGO on Alpine. If your build links C libraries, either set CGO_ENABLED=0 or use a Debian-based runtime image — a CGO binary will not start on plain Alpine.
scratch images have no CA certificates. If your app makes outbound HTTPS calls, copy /etc/ssl/certs in, or use alpine or distroless instead.

Configuration

If your Dockerfile is not at the repository root, point at it from .previewops.yaml:

provider: cloud-run
dockerfile: ./docker/Dockerfile
port: 8080
ttl_hours: 24

See configuration.md for every available option.

Do not gate startup behind a migration

Language-agnostic, and the hardest failure here to diagnose:

# Avoid this
CMD ["sh", "-c", "run-migrations && start-server"]

If the migration cannot reach the database — a paused instance, an expired connection string, a cold-start timeout — it never exits, the server never starts, and the port never opens. The deploy itself already succeeded, so the preview shows as Live while nothing answers. Run migrations as a separate, visible step instead.

getting-started.md — your first deploy end to end
configuration.md — .previewops.yaml reference
databases.md — connecting a database to a preview
ui-deploy.md — deploying from the dashboard