I have a container that links a volume to local path. This volume is used in script that is run by Dockerfile CMD.
I noticed that often this path does not exist at the time when CMD script is executed.
Is there anything I can do to guarantee that volume binding exist at time when CMD is run?
Example (although is trivial)
docker-compose:
...
volumes:
- /foo:/bar
...
script:
...
cat /bar/run.txt
...
Volumes work on container when you run it. CMD is Dockerfile command and it's about image building time. If you want to execute some scripts on image building stage you can add it by next command:
ADD localScript.sh /scriptForImage.sh
Related
I am migrating some web-apps to be managed via docker compose
It seems the docker-compose.yaml has a section for the container entry-point.
However, my individual docker files have an ENTRYPOINT themselves... should I remove this from the Dockerfiles? Does the entry-point in docker-compose override the Docker one?
You usually shouldn't specify entrypoint: or command: in a Compose file. Prefer specifying these in a Dockerfile. The one big exception is if you have a container that can do multiple things (for example, it can be both a Web server and a queue worker, with the same code) and you need to tell it with a command: to do not-the-default thing.
I'd suggest a typical setup like:
# docker-compose.yml
version: '3.8'
services:
app:
build: .
# with neither entrypoint: nor command:
# Dockerfile
FROM ...
WORKDIR /app
COPY ...
RUN ...
# ENTRYPOINT ["./entrypoint-wrapper.sh"]
CMD ["./my_app"]
Compose entrypoint: overrides the Dockerfile ENTRYPOINT and resets the CMD. Compose command: overrides the Dockerfile CMD.
In the Dockerfile both ENTRYPOINT and CMD are optional. If your base image already includes a correct command setup (nginx, php:fpm) then you can safely skip both.
It's otherwise somewhat a matter of style whether to use CMD or ENTRYPOINT in your Dockerfile. I prefer CMD for two reasons: it's easier to replace in a docker run ... image-name alternate command invocation, and there's a pattern of using ENTRYPOINT as a wrapper script to do first-time setup and then launch the CMD with exec "$#". If you have a JSON-array-syntax ENTRYPOINT then you can pass additional command-line arguments to it as docker run ... image-name --option. Both setups are commonplace.
The thing you shouldn't do is put an interpreter in ENTRYPOINT and a script name in CMD. I only ever see this in Python, but ENTRYPOINT ["python3"] is wrong. On the one hand this is hard to override in the same way ENTRYPOINT is in general, and on the other neither normal command override format works (you still have to repeat the script name if you want to run the same script with different options).
im unable to find an easy solution, but probably i'm just searching for the wrong things:
I have a docker-compose.yml which contains a tomcat that is built by the contents of the /tomcat folder. In /tomcat there is a Dockerfile, a .war and a server.xml.
The Dockerfile is based on tomcat:9, and copys the server.xml and .war files into the right directories.
If I do docker-compose up, everything is running fine. But i would love to find a way to update the connectors within the server.xml, without pruning the image, adjusting the server.xml and start it again.
It would be perfect to put a $CONNECTOR_CONFIG in the server.xml, and provide an variables.env to docker-compose where the $CONNECTOR_CONFIG variable is set to like ""
I know i could adjust the server.xml within the Dockerfile with sed, but this way the image must be pruned everytime i want to change something right?
Is there a way that i can later just edit the variables.env and docker-compose down/up?
Regards,
EdFred
A useful pattern here is to use the image's ENTRYPOINT as a wrapper script that does first-time setup. If that script ends with exec "$#" then it will execute the image's CMD as normal. You can use this to do things like rewrite configuration files based on environment variables.
#!/bin/sh
# docker-entrypoint.sh
# Replace any environment variable references in server.xml.tmpl.
# (Assumes the image has the full GNU tool set.)
envsubst <"$CATALINA_BASE/conf/server.xml.tmpl" >"$CATALINA_BASE/conf/server.xml"
# Run the standard container command.
exec "$#"
Normally in a tomcat image you wouldn't include a CMD since the base image knows how to start Tomcat. The Docker Hub tomcat image page has a mention of it, or you can click through to find the original Dockerfile. You need to know this since specifying an ENTRYPOINT in a derived Dockerfile will reset the CMD.
Your Dockerfile then needs to COPY this script in and set up the ENTRYPOINT and CMD.
# Dockerfile
FROM tomcat:9
COPY myapp.war /usr/local/tomcat/webapps/
COPY server.xml.tmpl /usr/local/tomcat/conf/
COPY docker-entrypoint.sh /usr/local/tomcat/bin/
# ENTRYPOINT _MUST_ be JSON-array form
ENTRYPOINT ["docker-entrypoint.sh"]
# Duplicate from base image
CMD ["catalina.sh", "run"]
You can verify this by hand using a docker run command. Any command you specify after the image name gets run instead of the CMD; but the main container command is still constructed by passing that command as arguments to the alternate ENTRYPOINT and so your wrapper script will run.
docker run --rm \
-e CONNECTOR_CONFIG=test-connector-config \
my-image \
cat /usr/local/tomcat/conf/server.xml
In your final Compose setup, you can include the configuration as an environment: variable.
version: '3.8'
services:
myapp:
build: .
ports: ['8080:8080']
environment:
CONNECTOR_CONFIG: ...
envsubst is a GNU tool that replaces $ENVIRONMENT_VARIABLE references in text files. It's very useful for this specific case, but you can do the same work with sed or another text-processing tool, especially if you don't have the GNU tools available (in particular if you have an Alpine-based image).
Maybe I'm just not understanding correctly but I'm trying to visually verify that I have used volumes properly.
In my docker-compose I'd have something like
some-project:
volumes:
- /some-local-path/some-folder:/v-test
I can verify it's contents via "ls -la /some-local-path/some-folder"
In some-projects Dockerfile I'd have something like
RUN ls -la /v-test
which returns 'No such file or directory"
Is this the correct way to use it? If so, why can't I view the contents from inside the container?
Everything in the Dockerfile runs before anything outside the build: block in the docker-compose.yml file is considered. The image build doesn't see volumes or environment variables that get declared only in docker-compose.yml, and it can't access other services.
In your example, first the Dockerfile tries to ls the directory, then Compose will start the container with the bind mount.
If you're just doing this for verification, you can docker-compose run a container with most of its settings from the docker-compose.yml file, but an alternate command:
docker-compose run some-project \
ls -la /v-test
(Doing this requires that the image's CMD is a well-formed shell command; either it has no ENTRYPOINT or the ENTRYPOINT is a wrapper script that ends in exec "$#" to run the CMD. If you only have ENTRYPOINT, change it to CMD; if you've split the command across both directives, consolidate it into a single CMD line.)
I am trying to build a docker image using the dockerfile, my purpose is to copy a file into a specific folder when i run the "docker run" command!
this my dockerfile code:
FROM openjdk:7
MAINTAINER MyPerson
WORKDIR /usr/src/myapp
ENTRYPOINT ["cp"]
CMD ["/usr/src/myapp"]
CMD ls /usr/src/myapp
After building my image without any error (using the docker build command), i tried to run my new image:
docker run myjavaimage MainClass.java
i got this error: ** cp: missing destination file operand after ‘MainClass.java’ **
How can i resolve this? thx
I think you want this Dockerfile:
FROM openjdk:7
WORKDIR /usr/src/myapp
COPY MainClass.java .
RUN javac MainClass.java
ENV CLASSPATH=/usr/src/myapp
CMD java MainClass
When you docker build this image, it COPYs your Java source file from your local directory into the image, compiles it, and sets some metadata telling the JVM where to find the resulting .class files. Then when you launch the container, it will run the single application you've packaged there.
It's common enough to use a higher-level build tool like Maven or Gradle to compile multiple files into a single .jar file. Make sure to COPY all of the source files you need in before running the build. In Java it seems to be common to build the .jar file outside of Docker and just COPY that in without needing a JDK, and that's a reasonable path too.
In the Dockerfile you show, Docker combines ENTRYPOINT and CMD into a single command and runs that command as the single main process of the container. If you provide a command of some sort at the docker run command, that overrides CMD but does not override ENTRYPOINT. You only get one ENTRYPOINT and one CMD, and the last one in the Dockerfile wins. So you're trying to run container processes like
# What's in the Dockerfile
cp /bin/sh -c "ls /usr/src/myapp"
# Via your docker run command
cp MainClass.java
As #QuintenScheppermans suggests in their answer you can use a docker run -v option to inject the file at run time, but this will happen after commands like RUN javac have already happened. You don't really want a workflow where the entire application gets rebuilt every time you docker run the container. Build the image during docker build time, or before.
Two things.
You have used CMD twice.
CMD can only be used once, think of it as the purpose of your docker image. Every time a container is run, it will always execute CMD if you want multiple commands, you should use RUN and then lastly, used CMD
FROM openjdk:
MAINTAINER MyPerson
WORKDIR /usr/src/
ENTRYPOINT ["cp"]
RUN /usr/src/myapp
RUN ls /usr/src/myapp
Copying stuff into image
There is a simple command COPY the syntax being COPY <from-here> <to-here>
Seems like you want to run myjavaimage so what you will do is
COPY /path/to/myjavaimage /myjavaimage
CMD myjavaimage MainClass.java
Where you see the arrows, I've just written dummy code. Replace that with the correct code.
Also, your Dockerfile is badly created.
ENTRYPOINT -> not sure why you'd do "cp", but it's an actual entrypoint. Could point to the root dir of your project or to an app that will be run.
Don't understand why you want to do ls /usr/src/myapp but if you do want to do it, use RUN and not CMD
Lastly,
Best way to debug docker containers are in interactive mode. That means ssh'ing in to your container, have a look around, run code, and see what is the problem.
Run this: docker run -it <image-name> /bin/bash and then have a look inside and it's usually the best way to see what causes issues.
This stackoverflow page perfectly answers your question.
COPY foo.txt /data/foo.txt
# where foo.txt is the relative path on host
# and /data/foo.txt is the absolute path in the image
If you need to mount a file when running the command:
docker run --name=foo -d -v ~/foo.txt:/data/foo.txt -p 80:80 image_name
Scripts or executables can run on a Docker container automatically when running docker-compose up --build with a configured Dockerfile containing syntax RUN, through which a script or executables etc. can run automatically during build.
Question: But is it possible to achieve the same goal, say run executables or scripts, with docker-compose only without a Dockerfile? In this case there are probably the similar command in docker-compose.yml like the RUN in Dockerfile ?
What you can do in docker-compose is overriding the default command that is executed after the build, by setting "command".
See here: https://docs.docker.com/compose/compose-file/#command
I don't think there is a RUN-like thing for docker-compose.yml.
if I understand your problem, then the answer is yes: on your container configuration in your docker-compose.yml file use:
entrypoint: ["/bin/sh","-c"]
command:
- |
ls -la
echo 'hello'
or whatever is your commands you want to run.