travis: optimize docker build

.travis.yml

@@ -10,6 +10,7 @@ services:
 env:
   global:
     - GO_FOR_RELEASE=1.11.x
+    - CGO_ENABLED=0
 go:
   - 1.11.x
   - tip
@@ -20,6 +21,7 @@ script:
   - unset GOPATH
   - export PATH=$PATH:$(go env GOPATH)/bin
   - make coverage
+  - go build -o video-transcoding-api
 after_success:
   - bash <(curl -s https://codecov.io/bash)
   - travis-scripts/docker.bash

Dockerfile.ci

@@ -0,0 +1,8 @@
+# This Dockerfile is intended to be used in the CI environment and depends on
+# an existing binary built outside Docker.
+
+FROM alpine:3.8
+
+RUN apk add --no-cache ca-certificates
+ADD video-transcoding-api /bin/video-transcoding-api
+CMD ["/bin/video-transcoding-api"]

travis-scripts/docker.bash

@@ -23,7 +23,7 @@ fi
 IMAGE_NAME=nytimes/video-transcoding-api
 
 docker login -u "${DOCKER_USERNAME}" -p "${DOCKER_PASSWORD}"
-docker build -t ${IMAGE_NAME}:latest .
+docker build -t ${IMAGE_NAME}:latest -f Dockerfile.ci .
 
 if [ -n "${TRAVIS_TAG}" ]; then
 	docker tag ${IMAGE_NAME}:latest ${IMAGE_NAME}:${TRAVIS_TAG}