Question 82011 in Docker Question posted in
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Keep docker container running in case of error

I have following docker file

FROM ruby:latest

# throw errors if Gemfile has been modified since Gemfile.lock
RUN bundle config --global frozen 1

WORKDIR /usr/src/app/

COPY Gemfile Gemfile.lock ./
RUN bundle install

ADD . /usr/src/app/

EXPOSE 3333

CMD ["ruby", "/usr/src/app/helloworld.rb"]

When I run image

docker run -t -d hello-world-ruby

Sinatra throws exception (which is OK), and container exits.

How can I keep it running so I can ssh into container and debug what’s happening?

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2

Answers


  1. 0

    A trick you can use is to start the application with a script.

    The following will work:

    FROM ruby:latest

# throw errors if Gemfile has been modified since Gemfile.lock
RUN bundle config --global frozen 1

WORKDIR /usr/src/app/

COPY Gemfile Gemfile.lock ./
RUN bundle install

ADD . /usr/src/app/

EXPOSE 3333

CMD [/usr/src/app/startup.sh]

    and in startup.sh, do:

    #!/bin/bash

ruby /usr/src/app/helloworld.rb &

sleep infinity

# or if you're on a version of linux that doesn't support bash and sleep infinity

while true; do sleep 86400; done

    chmod 755 and you should be set.

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  2. 0

    For debugging puproposes it is not needed to keep the container with a failing command alive, with loops or otherwise.

    To debug such issues just spawn a new container from the image with entrypoint/command as bash.

    docker run -it --name helloruby hello-world-ruby bash

    OR

    docker run -it --name helloruby --entrypoint bash hello-world-ruby

    This will give you shell inside the container where you can run/debug the ruby app

    ruby /usr/src/app/helloworld.rb
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