balancer: slightly improve docker layer caching (#1665)

Author: dyc3

deploy/balancer.Dockerfile

@@ -1,11 +1,8 @@
 FROM rust:1-slim-buster as build-stage
 
 WORKDIR /app/
-
-COPY . .
-
 RUN apt-get update && apt-get install -y build-essential pkg-config openssl libssl-dev && rm -rf /var/lib/apt/lists/*
-
+COPY . .
 RUN cargo build --release --bin ott-balancer-bin && mv ./target/release/ott-balancer-bin . && cargo clean
 
 FROM debian:buster-slim as production-stage

deploy/fly.prod.balancer.toml

@@ -3,6 +3,7 @@ primary_region = "ewr"
 
 [build]
 dockerfile = "balancer.Dockerfile"
+build-target = "deploy-stage"
 
 [build.args]
 DEPLOY_TARGET = "ott-balancer-prod"

deploy/fly.staging.balancer.toml

@@ -3,6 +3,7 @@ primary_region = "ewr"
 
 [build]
 dockerfile = "balancer.Dockerfile"
+build-target = "deploy-stage"
 
 [build.args]
 DEPLOY_TARGET = "ott-balancer-staging"