Unify Dockerfiles, allow cross-compiling within Docker

build/docker/Dockerfile

@@ -0,0 +1,36 @@
+# The binary to build the image around (monolith or polylith).
+ARG DENDRITE_BINARY
+
+FROM --platform=$BUILDPLATFORM docker.io/golang:alpine AS base
+ARG TARGETARCH
+ARG DENDRITE_BINARY 
+ENV GOARCH=$TARGETARCH
+ENV CGO_ENABLED=1
+# The host triple of the *builder container.* Will end in musl because Alpine. E.g. aarch64-linux-musl.
+# Only relevant when cross-compiling.
+ARG HOST_TRIPLE="x86_64-linux-musl"
+
+# Todo: Do we *really* need rsync?
+RUN apk --update --no-cache add bash build-base curl rsync
+
+WORKDIR /build
+COPY . /build
+
+RUN bash ./build/docker/cross-helper.sh dl-compiler
+
+RUN mkdir -p bin
+RUN CC=$(./build/docker/cross-helper.sh cc) go build -trimpath -o bin/ ./cmd/$DENDRITE_BINARY
+RUN CC=$(./build/docker/cross-helper.sh cc) go build -trimpath -o bin/ ./cmd/goose
+RUN CC=$(./build/docker/cross-helper.sh cc) go build -trimpath -o bin/ ./cmd/create-account
+RUN CC=$(./build/docker/cross-helper.sh cc) go build -trimpath -o bin/ ./cmd/generate-keys
+
+FROM alpine:latest
+ARG DENDRITE_BINARY
+ENV DENDRITE_BINARY=$DENDRITE_BINARY
+
+COPY --from=base /build/bin/* /usr/bin/
+
+VOLUME /etc/dendrite
+WORKDIR /etc/dendrite
+
+ENTRYPOINT ["/usr/bin/$DENDRITE_BINARY"]

build/docker/Dockerfile.monolith

@@ -1,22 +0,0 @@
-FROM docker.io/golang:1.15-alpine AS base
-
-RUN apk --update --no-cache add bash build-base
-
-WORKDIR /build
-
-COPY . /build
-
-RUN mkdir -p bin
-RUN go build -trimpath -o bin/ ./cmd/dendrite-monolith-server
-RUN go build -trimpath -o bin/ ./cmd/goose
-RUN go build -trimpath -o bin/ ./cmd/create-account
-RUN go build -trimpath -o bin/ ./cmd/generate-keys
-
-FROM alpine:latest
-
-COPY --from=base /build/bin/* /usr/bin
-
-VOLUME /etc/dendrite
-WORKDIR /etc/dendrite
-
-ENTRYPOINT ["/usr/bin/dendrite-monolith-server"]

build/docker/Dockerfile.polylith

@@ -1,22 +0,0 @@
-FROM docker.io/golang:1.15-alpine AS base
-
-RUN apk --update --no-cache add bash build-base
-
-WORKDIR /build
-
-COPY . /build
-
-RUN mkdir -p bin
-RUN go build -trimpath -o bin/ ./cmd/dendrite-polylith-multi
-RUN go build -trimpath -o bin/ ./cmd/goose
-RUN go build -trimpath -o bin/ ./cmd/create-account
-RUN go build -trimpath -o bin/ ./cmd/generate-keys
-
-FROM alpine:latest
-
-COPY --from=base /build/bin/* /usr/bin
-
-VOLUME /etc/dendrite
-WORKDIR /etc/dendrite
-
-ENTRYPOINT ["/usr/bin/dendrite-polylith-multi"]

build/docker/README.md

@@ -7,13 +7,15 @@ They can be found on Docker Hub:
 - [matrixdotorg/dendrite-monolith](https://hub.docker.com/r/matrixdotorg/dendrite-monolith) for monolith deployments
 - [matrixdotorg/dendrite-polylith](https://hub.docker.com/r/matrixdotorg/dendrite-polylith) for polylith deployments
 
-## Dockerfiles
+## Building the image
 
-The `Dockerfile` builds the base image which contains all of the Dendrite
-components. The `Dockerfile.component` file takes the given component, as
-specified with `--buildarg component=` from the base image and produce
-smaller component-specific images, which are substantially smaller and do
-not contain the Go toolchain etc.
+The `Dockerfile` can build both monolith and polylith images for Dendrite.
+To choose which is selected, set `--build-arg DENDRITE_BINARY=$binary`,
+where `$binary` is `dendrite-monolith-server` or `dendrite-polylith-multi`
+for monolith or polylith respectively.
+
+Note that you **must** use BuildKit to build the images. You can enable
+it for the build with `DOCKER_BUILDKIT=1 docker build [...]`
 
 ## Compose files
 

build/docker/cross-helper.sh

@@ -0,0 +1,59 @@
+#!/bin/bash
+set -eu
+
+# Utility script for getting and using cross-compilation toolchains in Docker.
+# You really shouldn't run this outside of a container, though there's no reason you can't.
+
+# $1 is used for arch
+function install_musl() {
+    rm musl.tgz
+    cd ${1}-cross
+    rm -f $(find . -name "ld-musl-*.so.1")
+    rm usr
+    # error supression!
+    rsync --ignore-errors -rLaq . / || true
+    cd ..
+    rm -rf ${1}-cross
+}
+
+function get_triple() {
+    case "${1}" in
+    "arm64")
+        echo "aarch64-linux-musl"
+        ;;
+    "arm")
+        echo "arm-linux-musleabi"
+        ;;
+    "amd64")
+        echo "x86_64-linux-musl"
+        ;;
+    *)
+        exit 1
+        ;;
+    esac
+}
+
+arch=$(go env GOARCH)
+
+case "${1}" in
+"dl-compiler")
+    if [[ "${arch}" == "$(go env GOHOSTARCH)" ]]; then
+        echo "not cross-compiling, nothing to do"
+        exit 0
+    fi
+    MUSLCC_BASE="https://more.musl.cc/${HOST_TRIPLE}"
+    target="$(get_triple ${arch})"
+    curl "${MUSLCC_BASE}/${target}-cross.tgz" -o musl.tgz
+    tar xzf musl.tgz
+    install_musl ${target}
+    ;;
+"cc")
+    if [[ ${arch} == "$(go env GOHOSTARCH)" ]]; then
+        echo "gcc"
+    else
+        echo "$(get_triple $(go env GOARCH))-gcc"
+    fi
+    ;;
+*)
+    exit 1
+esac