Switched to alpine-based Docker build

Dockerfile

@@ -1,17 +1,33 @@
-# syntax=docker/dockerfile:1.2
-FROM rustlang/rust:nightly AS builder
+FROM rust:alpine AS builder
+
+# Switch to the nightly build
+RUN rustup default nightly
 
 WORKDIR /usr/src/app
 
-# Build the app
-COPY . .
-RUN --mount=type=cache,target=/usr/src/app/target cargo install --path .
+# Install build dependencies & create a new dummy project
+# that we use as a build cache
+RUN apk update && \
+    apk add --no-cache openssl openssl-dev musl-dev && \
+    cargo init --bin
+
+# Build the dependencies
+# This is done separately to reduce average compile time
+# Afterwards, we remove the dummy src directory
+COPY Cargo.toml Cargo.lock .
+RUN cargo build --release && \
+    rm src/*.rs
+
+# Now, we build our own source code
+COPY src/ ./src
+RUN cargo install --path .
 
 
-FROM debian:buster-slim
+# Now, we create the actual image
+FROM alpine:latest
 
 # Install dependencies
-RUN apt update && apt install -y openssl
+RUN apk update && apk add --no-cache openssl
 
 COPY --from=builder /usr/local/cargo/bin/rust-api /usr/local/bin/rust-api