Try using cargo chef.

tests/integration/Dockerfile

@@ -2,8 +2,56 @@
 # License, v. 2.0. If a copy of the MPL was not distributed with this
 # file, You can obtain one at http://mozilla.org/MPL/2.0/.
 
+# =============================================================================
+# Pull in the version of cargo-chef we plan to use, so that all the below steps
+# use a consistent set of versions.
+FROM lukemathwalker/cargo-chef:0.1.68-rust-slim-bookworm AS chef
+WORKDIR /app
+
+# =============================================================================
+# Analyze the project, and produce a plan to compile its dependcies. This will
+# be run every time. The output should only change if the dependencies of the
+# project change, or if significant details of the build process change.
+FROM chef AS planner
+COPY . .
+RUN cargo chef prepare --recipe-path recipe.json
+
+# =============================================================================
+# Use the plan from above to build only the dependencies of the project. This
+# should almost always be pulled straight from cache unless dependencies or the
+# build process change.
+FROM chef AS cacher
+COPY --from=planner /app/recipe.json recipe.json
+
+RUN \
+    apt-get -qq update && \
+    apt-get -qq install --no-install-recommends -y \
+      cmake libssl-dev ca-certificates pkg-config build-essential
+
+RUN cargo chef cook --recipe-path recipe.json
+
+# =============================================================================
+# Now build the project, taking advantage of the cached dependencies from above.
+FROM chef AS builder
+ARG APT_CACHE_BUST
+
+RUN mkdir -m 755 bin
+RUN apt-get -qq update && \
+    apt-get -qq upgrade && apt-get -qq install --no-install-recommends -y \
+      cmake libssl-dev ca-certificates libstdc++6 libstdc++-12-dev
+RUN cargo --version && \
+    rustc --version
+COPY . .
+COPY --from=cacher /app/target target
+COPY --from=cacher $CARGO_HOME $CARGO_HOME
+
+RUN cargo build --features=emulator
+
 FROM python:3.12-slim-bookworm
 
+# =============================================================================
+# Setup Integration test image
+
 LABEL org.opencontainers.image.authors="[email protected]"
 
 ENV LANG=C.UTF-8
@@ -19,25 +67,14 @@ ENV DB_DSN=grpc://localhost:8086
 # (g++/make for gevent on pypy)
 RUN apt-get update && apt install -y --no-install-recommends \
     git \
-    gpg \
     build-essential \
-    python3-dev \
     curl \
-    libstdc++6 \
-    libstdc++-12-dev \
-    libssl-dev \
-    pkg-config \
-    cmake
 
 RUN python -m venv ${PYTHON_VENV}
 ENV PATH="${PYTHON_VENV}/bin:${PATH}"
 
 RUN python -m pip install --upgrade pip
 
-# Install Rust
-RUN curl https://sh.rustup.rs -sSf | sh -s -- --default-toolchain 1.81 -y
-RUN rustc --version
-
 # Setup poetry and install requirements
 ENV POETRY_VIRTUALENVS_CREATE=false \
   POETRY_VERSION=1.7.0
@@ -52,10 +89,10 @@ RUN apt-get update -y && apt install google-cloud-cli-cbt -y
 
 COPY . /code
 
-WORKDIR /code
+COPY --from=builder /app/target/debug /code/target/debug
+COPY --from=builder /app/version.json /code
 
-# Build app
-RUN cargo build --features=emulator
+WORKDIR /code
 
 RUN chmod +x scripts/setup_bt.sh