Improve docker image creation

docker/.dockerignore

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+# Ignore common build artifacts and large nix store paths
+result
+result.tar.gz
+result-*.tar.gz
+dist
+dist-newstyle
+dist/*
+*.o
+*.hi
+.stack-work
+.ghc.environment.*
+.cabal-sandbox
+.cabal-sandbox/*
+node_modules
+.git
+*.lock
+**/.DS_Store
+
+# Ignore Nix store references and temporary files
+/nix
+*.drv
+*.nar
+

docker/Dockerfile

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+# Lightweight Dockerfile for a static cardano-db-sync binary
+#
+# Usage (example):
+# 1. Build a static executable with Nix:
+#      nix build .#cardano-db-sync-linux
+# 2. Build the image from the project root:
+#      docker build -f docker/Dockerfile -t cardano-db-sync:lightweight .
+#
+# Note: Since result/ is a Nix symlink, Docker may have issues following it.
+# If this fails, you can dereference the symlink first:
+#      mkdir -p docker/build && cp -L result/*.tar.gz docker/build/
+#      docker build -f docker/Dockerfile -t cardano-db-sync:lightweight .
+#
+# Important: this Dockerfile assumes the binary is a fully static executable
+# (statically linked). If it's not static, use a small base image (see docs).
+
+# Stage 1: Extract the binary from the tarball
+FROM busybox:latest AS extractor
+ARG TARBALL
+# ADD automatically extracts tarballs
+ADD ${TARBALL} /tmp/extract/
+RUN find /tmp/extract -name cardano-db-sync -type f -exec mv {} /cardano-db-sync \; && \
+    chmod +x /cardano-db-sync
+
+# Stage 2: Minimal runtime image
+FROM scratch
+COPY --from=extractor /cardano-db-sync /usr/local/bin/cardano-db-sync
+ENTRYPOINT ["/usr/local/bin/cardano-db-sync"]
+CMD ["--help"]

docker/README.md

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+Lightweight Docker image for cardano-db-sync
+==========================================
+
+This folder contains a minimal Docker context and `Dockerfile` intended for use with
+a statically-built `cardano-db-sync` executable produced by Nix.
+
+Why this exists
+---------------
+
+Building the full NixOS-based Docker image is a reproducible approach, but can lead
+to large images and bundled configuration that make customization more difficult.
+This lightweight approach lets users build a small, standard Docker image and supply
+configuration at runtime via volumes or create their own derived images.
+
+Quickstart
+----------
+
+1. Build the cardano-db-sync package with Nix:
+
+   ```bash
+   nix build .#cardano-db-sync-linux
+   ```
+
+2. a) Extract the binary from the tarball and copy it to this directory:
+
+   ```bash
+   tar xf result/cardano-db-sync-*-linux.tar.gz -C docker/ --strip-components=1 ./bin/cardano-db-sync
+   ```
+
+2. b) move the binary:
+
+   ```bash
+   mv docker/bin/cardano-db-sync ./docker && rm -r docker/bin/
+   ```
+
+3. Build the image:
+
+   ```bash
+   docker build -t cardano-db-sync:lightweight docker/
+   ```
+
+4. get the configs:
+- https://book.world.dev.cardano.org/environments/preprod/db-sync-config.json
+
+4. Run the container and mount your configuration (recommended):
+
+   ```bash
+   docker run -v $PWD/environments/preprod:/config \
+     --env POSTGRES_HOST=postgres --env POSTGRES_PORT=5432 \
+     cardano-db-sync:lightweight --config $PWD/config/db-sync-config.json \
+     --socket-path "$HOME/workshop/cardano-node/configuration/preprod/db/node.socket" \
+     --schema-dir /schema
+   ```
+
+Notes
+-----
+
+- The `Dockerfile` uses `FROM scratch` and therefore requires the binary to be
+  statically linked. If you need dynamic linking, change the base image to a small
+  distro such as `ubuntu:24.04` or `debian:bookworm-slim`.
+- The image intentionally omits network configuration files. Use volumes or a
+  derived image if you want to embed configs.
+
+See also: the project's `doc/docker.md` for more details and guidance.
+

docker/build.sh

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+#!/usr/bin/env bash
+set -euo pipefail
+
+# Dereference the Nix result symlink
+TARBALL=$(basename "$(readlink -f result/*.tar.gz)")
+cp -L result/*.tar.gz docker/
+
+# Build with the exact tarball name as build arg
+docker build --build-arg TARBALL="$TARBALL" -t cardano-db-sync:lightweight docker/
+
+# Cleanup
+rm -f docker/*.tar.gz