fix: don't use adduser and addgroup for docker images (#3344)

* fix: don't use adduser and addgroup for docker images

* Revert "fix: Remove alternative image architectures until we virtualize (#3336)"

This reverts commit 00c5116a2e.

Dockerfile

@@ -1,4 +1,8 @@
-FROM alpine
+# This is the multi-arch Dockerfile used for Coder. Since it's multi-arch and
+# cross-compiled, it cannot have ANY "RUN" commands. All binaries are built
+# using the go toolchain on the host and then copied into the build context by
+# scripts/build_docker.sh.
+FROM alpine:latest
 
 # LABEL doesn't add any real layers so it's fine (and easier) to do it here than
 # in the build script.
@@ -11,12 +15,12 @@ LABEL \
 	org.opencontainers.image.version="$CODER_VERSION" \
 	org.opencontainers.image.licenses="AGPL-3.0"
 
+# Create coder group and user. We cannot use `addgroup` and `adduser` because
+# they won't work if we're building the image for a different architecture.
+COPY --chown=root:root --chmod=644 group passwd /etc/
+
 # The coder binary is injected by scripts/build_docker.sh.
-ADD coder /opt/coder
+COPY --chown=coder:coder --chmod=755 coder /opt/coder
 
-# Create coder group and user.
-RUN addgroup -g 1000 coder && \
-	adduser -D -g "" -h /home/coder -G coder -u 1000 -S -s /bin/sh coder
 USER coder:coder
-
 ENTRYPOINT [ "/opt/coder", "server" ]