Unable to Read Files in Container - docker

Question

Here is my docker-compose.yml:
version: '3.3'
services:
etcd:
container_name: 'etcd'
image: 'quay.io/coreos/etcd'
command: >
etcd -name etcd
-advertise-client-urls http://127.0.0.1:2379,http://127.0.0.1:4001
-listen-client-urls http://0.0.0.0:2379,http://0.0.0.0:4001
-initial-advertise-peer-urls http://127.0.0.1:2380
-listen-peer-urls http://0.0.0.0:2380
healthcheck:
test: ["CMD", "curl", "-f", "http://etcd:2379/version"]
interval: 30s
timeout: 10s
retries: 5
networks:
robotrader:
kontrol:
container_name: 'kontrol'
env_file: 'variables.env'
build:
context: '.'
dockerfile: 'Dockerfile'
volumes:
- '/certs:/certs'
ports:
- '6000:6000'
depends_on:
- 'etcd'
networks:
robotrader:
mongo:
container_name: 'mongo'
image: 'mongo:latest'
ports:
- '27017:27017'
volumes:
- '/var/lib/mongodb:/var/lib/mongodb'
networks:
robotrader:
networks:
robotrader:
... and here is the Dockerfile used to build kontrol:
FROM golang:1.8.3 as builder
RUN go get -u github.com/golang/dep/cmd/dep
RUN go get -d github.com/koding/kite
WORKDIR ${GOPATH}/src/github.com/koding/kite
RUN ${GOPATH}/bin/dep ensure
RUN go install ./kontrol/kontrol
RUN mv ${GOPATH}/bin/kontrol /tmp
FROM busybox
ENV APP_HOME /opt/robotrader
RUN mkdir -p ${APP_HOME}
RUN mkdir /certs
WORKDIR ${APP_HOME}
COPY --from=builder /tmp/kontrol .
ENTRYPOINT ["./kontrol", "-initial"]
CMD ["./kontrol"]
Finally when I issue the command...
sudo -E docker-compose -f docker-compose.yaml up
... both etcd and mongo start successfully, whereas kontrol fails with the following error:
kontrol | 2018/06/21 20:11:14 cannot read public key file: open "/certs/key_pub.pem": no such file or directory
If I log into the container..
sudo docker run -it --rm --name j3d-test --entrypoint sh j3d
... and look at folder /certs, the files are there:
ls -la /certs
-rw-r--r--. 1 root root 1679 Jun 21 21:11 key.pem
-rw-r--r--. 1 root root 451 Jun 21 21:11 key_pub.pem
What am I missing?

Answer 1

When you run this command:
sudo docker run -it --rm --name j3d-test --entrypoint sh j3d
You are not "logging into the container". You are creating a new container, and you are looking at the contents of /certs on the underlying image. However, in your docker-compose.yaml you have:
kontrol:
[...]
volumes:
- '/certs:/certs'
[...]
You have configured a bind mount from $PWD/certs onto the /certs
directory in your container. What does your local certs directory
contain?