对Dockerfile中的CMD / ENTRYPOINT感到困惑

Question

I am unsure what to use for ENTRYPOINT vs CMD for my Dockerfile below.

FROM mongo:3.4-xenial

RUN apt-get update
RUN apt-get install -y software-properties-common
RUN apt-get install zip \
    unzip
RUN apt-get install -y default-jdk
RUN apt-get update -y && \
    apt-get clean

RUN mkdir -p /opt/project

COPY ./project-repo/target/project-repo.zip /opt/project

WORKDIR /opt/project 
RUN unzip project-repo.zip

ENTRYPOINT echo '#!/bin/bash\n\
    pidfile="${TMPDIR:-/tmp}/docker-entrypoint-temp-mongod.pid" \n\
    rm -f "$pidfile" \n\
    # start MongoDB here \n\
    mongod --logpath /var/log/mongodb.log --dbpath /data/db/ --fork --pidfilepath "$pidfile" \n\
    mongo=( mongo --host 127.0.0.1 --port 27017 --quiet ) \n\
    # check to see that our "mongod" actually did start up (catches "--help", "--version", MongoDB 3.2 being silly, slow prealloc, etc) \n\
    # https://jira.mongodb.org/browse/SERVER-16292 \n\
    tries=30 \n\
    while true; do \n\
        if ! { [ -s "$pidfile" ] && ps "$(< "$pidfile")" &> /dev/null; }; then \n\
            # bail ASAP if "mongod" is not even running \n\
            echo >&2 \n\
            echo >&2 "error: mongod does not appear to have stayed running -- perhaps it had an error?" \n\
            echo >&2 \n\
            exit 1 \n\
        fi \n\
        if mongo admin --eval "quit(0)" &> /dev/null; then \n\
            # success! \n\
            break \n\
        fi \n\
        (( tries-- )) \n\
        if [ "$tries" -le 0 ]; then \n\
            echo >&2 \n\
            echo >&2 "error: mongod does not appear to have accepted connections quickly enough -- perhaps it had an error?" \n\
            echo >&2 \n\
            exit 1 \n\
        fi \n\
        sleep 1 \n\
    done \n\
    mongo -- admin <<-EOF \n\
    db.createUser({user:"user", pwd:"admin123", roles:[{role:"root", db:"admin"}]}); \n\
EOF' >> ./init_mongo.sh && chmod +x ./init_mongo.sh && ./init_mongo.sh && \
    chmod +x /opt/project/setup.sh && /opt/project/setup.sh all && \
    chmod +x /opt/project/start.sh && /opt/project/start.sh all

EXPOSE 8080

CMD ["echo 'Welcome to Demo'"]

My MongoDB initialization is based on the one supplied with the standard image. They use mongod as the CMD .

I need a few things - start mongo, create the user then run my scripts - setup and start.

There are no errors. However, after ENTRYPOINT finishes doing its' thing, the container just exits. I want it to stay running!!!

My guess that my CMD is wrong. Please advise.

Thank you

Answer 1

After ENTRYPOINT finishes doing it's thing, the container just exits.

This is a universal truth: the lifetime of a container is exactly the lifetime of the ENTRYPOINT , or absent one, the CMD .

In terms of style, don't try writing very long scripts like that inline in a Dockerfile. Make it be a separate file, COPY it into the image, make sure it's executable, and just run it directly.

The other style point is that it's very useful to get a debugging shell in a built image like

docker run --rm -it imagename bash

But, that form only overwrites the CMD . That means you should generally put the command you want to run in CMD exclusively. Since this will be the main container process, it must be something that stays running for as long as the container will be; it can't be something like start.sh or service start that tries to launch it in the background and immediately returns. For example,

CMD ["/opt/project/myservice", "--foreground"]

What good is ENTRYPOINT , then? If you have both ENTRYPOINT and CMD , the ENTRYPOINT will get run with the CMD as command-line arguments. A very common pattern is to write a script that does some initial setup, then does exec "$@" to run the command part. From your example,

#!/bin/sh
./init_mongo.sh
exec "$@"

And your combined Dockerfile could look more or less like

FROM ubuntu:18.04
# ... other setup bits ...
WORKDIR /opt/project
COPY entrypoint.sh init_mongo.sh .
RUN chmod +x entrypoint.sh init_mongo.sh
ENTRYPOINT ["/opt/project/entrypoint.sh"]
CMD ["/opt/project/myservice", "--foreground"]