I'm trying to understand volumes.
When I build and run this image with docker build -t myserver . and docker run -dp 8080:80 myserver, the web server on it prints "Hallo". When I change "Hallo" to "Huhu" in the Dockerfile and rebuild & run the image/container, it shows "Huhu". So far, no surprises.
Next, I added a docker-compose.yaml file that has two volumes. One volume is mounted on an existing path of where the Dockerfile creates the index.html. The other is mounted on a new and unused path. I build and run everything with docker compose up --build.
On the first build, the web server prints "Hallo" as expected. I can also see the two volumes in Docker GUI and its contents. The index.html that was written to the image, is now present in the volume. (I guess the volume gets mounted before the Dockerfile can write to it.)
On the second build (swap "Hallo" with "huhu" and run docker compose up --build again) I was expecting the webserver to print "Huhu". But it prints "Hallo". So I'm not sure why the data on the volume was not overwritten by the Dockerfile.
Can you explain?
Here are the files:
Dockerfile
FROM nginx
# First build
RUN echo "Hallo" > /usr/share/nginx/html/index.html
# Second build
# RUN echo "Huhu" > /usr/share/nginx/html/index.html
docker-compose.yaml
services:
web:
build: .
ports:
- "8080:80"
volumes:
- html:/usr/share/nginx/html
- persistent:/persistent
volumes:
html:
persistent:
There are three different cases here:
When you build the image, it knows nothing about volumes. Whatever string is in that RUN echo line, it is stored in the image. Volumes are not mounted when you run the docker-compose build step, and the Dockerfile cannot write to a volume at all.
The first time you run a container with the volume mounted, and the first time only, if the volume is empty, Docker copies content from the mount point in the image into the volume. This only happens with named volumes and not bind mounts; it only happens on native Docker and not Kubernetes; the volume content is never updated at all after this happens.
The second time you run a container with the volume mounted, since the volume is already populated, the content from the volume hides the content in the image.
You routinely see various cases that uses named volumes to "pass through" to the image (especially Node applications) or to "share files" with another container (frequently an Nginx server). These only work because Docker (and only Docker) automatically populates empty named volumes, and therefore they only work the first time. If you change your package.json, your Node application that mounts a volume over node_modules won't see updates; if you change your static assets that you're sharing with a Web server, the named volume will hide those changes in both the application and HTTP-server containers.
Since the named-volume auto-copy only happens in this one very specific case, I'd try to avoid using it, and more generally try to avoid mounting anything over non-empty directories in your image.
Pretty much the title says it all.
I know I can copy the file (from the host) into a docker container.
I also know I can copy the directory into a docker container.
But how to copy the contents of a directory (preserving all subdirectories) into a directory in a docker container?
On my host I have a directory called src. On the docker container I have a directory /var/www/html. That src has both files and directories. I need all of them to be copied (with the command) into the container; not bound, not mounted, but copied.
It sounds like a trivial operation, but I've tried so many ways and couldn't find anything online that works! Ideally, it would be best if that copy operation would work every time I run the docker-compose up -d command.
Thanks in advance!
I found the solution. There is a way of specifying the context directory explicitly; in that case the dockerfile also need to be specified explicitly too.
In the docker-compose.yml one should have the following structure:
services:
php:
build:
context: .
dockerfile: ./php/Dockerfile
In this case the src is "visible" because it is inside the context! Then in that Dockerfile the COPY command will work!
Update: There is another way to achieve this via the command as well. However for me it started to work when I've added the ./ at the end. So the full command is:
docker cp ./src/./ $(docker-compose ps|grep php|awk '{print $1}'):/var/www/html/
I am checking the docker documentation on how to use named volumes to share data between containers.
In Populate a volume using a container it is specified that:
If you start a container which creates a new volume, as above, and the container has files or directories in the directory to be mounted (such as /app/ above), the directory’s contents are copied into the volume. The container then mounts and uses the volume, and other containers which use the volume also have access to the pre-populated content.
So I did a simple example where:
I start a container which creates the volume and mounts it to a directory with existing files
I start a second container on which I mount the volume and indeed I can see the first container's files.
So far so good.
However I wanted to see if it is possible to have pre-populated content from more than one containers.
What I did was
Create two simple images which have their respective configuration files in the same directory
FROM alpine:latest
WORKDIR /opt/test
RUN mkdir -p "/opt/test/conf" && \
echo "container from image 1" > /opt/test/conf/config_1.cfg
FROM alpine:latest
WORKDIR /opt/test
RUN mkdir -p "/opt/test/conf" && \
echo "container from image 2" > /opt/test/conf/config_2.cfg
Create a docker compose which defines a named volume which is mounted on both services
services:
test_container_1:
image:
test_image_1
volumes:
- test_volume:/opt/test/conf
tty: true
test_container_2:
image:
test_image_2
volumes:
- test_volume:/opt/test/conf
tty: true
volumes:
test_volume:
Started the services.
> docker-compose -p example up
Creating network "example_default" with the default driver
Creating volume "example_test_volume" with default driver
Creating example_test_container_2_1 ... done
Creating example_test_container_1_1 ... done
Attaching to example_test_container_1_1, example_test_container_2_1
According to the logs container_2 was created first and it pre-populated the volume. However, the volume was then mounted to container_1 and the only file available on the mount was apparently /opt/test/conf/config_2.cfg effectively removing config_1.
So my question is, if it is possible to have a volume populated with data from 2 or more containers.
The reason I want to explore this, is so that I can have additional app configuration loaded from different containers, to support a multi tenant scenario, without having to rework the app to read the tenant configuration from different folders.
Thank you in advance
Once there is any content in a named volume at all, Docker will never automatically copy content into it. It will not merge content from two different images, update the volume if one of the images changes, or anything else.
I'd advise you to ignore the paragraph you quote in the Docker documentation. Assume any volume you mount into the container is initially empty. This matches the behavior you'll get with Docker bind-mounts (host directories), Kubernetes persistent volumes, and basically any other kind of storage besides Docker named volumes proper. Don't mount a volume over the content in your image.
If you can, restructure your application to avoid sharing files at all. One common use of named volumes I see is trying to republish static assets to a reverse proxy, for example; rather than trying to use a named volume (which will never update itself) you can COPY the static assets into a dedicated Web server image. This avoids the various complexities around trying to use a volume here.
If you really don't have a choice in the matter, then you can approach this with dedicated code in both of the containers. The basic setup here is:
Have a data directory somewhere outside your application directory, and mount the volume there.
Include the original files in the image somewhere different.
In an entrypoint wrapper script, copy the original files into the data directory (the mounted volume).
Let's say for the sake of argument that you've installed the application into /opt/test, and the data directory will be /etc/test. The entrypoint wrapper script can be as little as
#!/bin/sh
# Copy config files from the application tree into the config tree
# (overwriting anything that's already there)
cp /opt/test/* "$TEST_CONFIG_DIR"
# Run the main container command
exec "$#"
In the Dockerfile, you need to make sure that directory exists (and if you'll use a non-root user, that user needs permission to write to it).
FROM alpine
WORKDIR /opt/test
COPY ./ ./
ENV TEST_CONFIG_DIR=/etc/test
RUN mkdir "$TEST_CONFIG_DIR"
ENTRYPOINT ["./entrypoint.sh"]
CMD ["./my_app"]
Finally, in the Compose setup, mount the volume on that data directory (you can't use the environment variable, but consider the filesystem path part of the image's API):
version: '3.8'
volumes:
test_config:
services:
one:
build: ./one
volumes:
- test_config:/etc/test
two:
build: ./two
volumes:
- test_config:/etc/test
You would be able to run, for example,
docker-compose run one ls /etc/test
docker-compose run two ls /etc/test
to see both sets of files appear there.
The entrypoint script is code you control. There's nothing especially magical about it beyond the final exec "$#" line to run the main container command. If you want to ignore files that already exist, for example, or if you have a way to merge in changes, then you can implement something more clever than a simple cp command.
How can I include files from outside of Docker's build context using the "ADD" command in the Docker file?
From the Docker documentation:
The path must be inside the context of the build; you cannot ADD
../something/something, because the first step of a docker build is to
send the context directory (and subdirectories) to the docker daemon.
I do not want to restructure my whole project just to accommodate Docker in this matter. I want to keep all my Docker files in the same sub-directory.
Also, it appears Docker does not yet (and may not ever) support symlinks: Dockerfile ADD command does not follow symlinks on host #1676.
The only other thing I can think of is to include a pre-build step to copy the files into the Docker build context (and configure my version control to ignore those files). Is there a better workaround for than that?
The best way to work around this is to specify the Dockerfile independently of the build context, using -f.
For instance, this command will give the ADD command access to anything in your current directory.
docker build -f docker-files/Dockerfile .
Update: Docker now allows having the Dockerfile outside the build context (fixed in 18.03.0-ce). So you can also do something like
docker build -f ../Dockerfile .
I often find myself utilizing the --build-arg option for this purpose. For example after putting the following in the Dockerfile:
ARG SSH_KEY
RUN echo "$SSH_KEY" > /root/.ssh/id_rsa
You can just do:
docker build -t some-app --build-arg SSH_KEY="$(cat ~/file/outside/build/context/id_rsa)" .
But note the following warning from the Docker documentation:
Warning: It is not recommended to use build-time variables for passing secrets like github keys, user credentials etc. Build-time variable values are visible to any user of the image with the docker history command.
I spent a good time trying to figure out a good pattern and how to better explain what's going on with this feature support. I realized that the best way to explain it was as follows...
Dockerfile: Will only see files under its own relative path
Context: a place in "space" where the files you want to share and your Dockerfile will be copied to
So, with that said, here's an example of the Dockerfile that needs to reuse a file called start.sh
Dockerfile
It will always load from its relative path, having the current directory of itself as the local reference to the paths you specify.
COPY start.sh /runtime/start.sh
Files
Considering this idea, we can think of having multiple copies for the Dockerfiles building specific things, but they all need access to the start.sh.
./all-services/
/start.sh
/service-X/Dockerfile
/service-Y/Dockerfile
/service-Z/Dockerfile
./docker-compose.yaml
Considering this structure and the files above, here's a docker-compose.yml
docker-compose.yaml
In this example, your shared context directory is the runtime directory.
Same mental model here, think that all the files under this directory are moved over to the so-called context.
Similarly, just specify the Dockerfile that you want to copy to that same directory. You can specify that using dockerfile.
The directory where your main content is located is the actual context to be set.
The docker-compose.yml is as follows
version: "3.3"
services:
service-A
build:
context: ./all-service
dockerfile: ./service-A/Dockerfile
service-B
build:
context: ./all-service
dockerfile: ./service-B/Dockerfile
service-C
build:
context: ./all-service
dockerfile: ./service-C/Dockerfile
all-service is set as the context, the shared file start.sh is copied there as well the Dockerfile specified by each dockerfile.
Each gets to be built their own way, sharing the start file!
On Linux you can mount other directories instead of symlinking them
mount --bind olddir newdir
See https://superuser.com/questions/842642 for more details.
I don't know if something similar is available for other OSes.
I also tried using Samba to share a folder and remount it into the Docker context which worked as well.
If you read the discussion in the issue 2745 not only docker may never support symlinks they may never support adding files outside your context. Seems to be a design philosophy that files that go into docker build should explicitly be part of its context or be from a URL where it is presumably deployed too with a fixed version so that the build is repeatable with well known URLs or files shipped with the docker container.
I prefer to build from a version controlled source - ie docker build
-t stuff http://my.git.org/repo - otherwise I'm building from some random place with random files.
fundamentally, no.... -- SvenDowideit, Docker Inc
Just my opinion but I think you should restructure to separate out the code and docker repositories. That way the containers can be generic and pull in any version of the code at run time rather than build time.
Alternatively, use docker as your fundamental code deployment artifact and then you put the dockerfile in the root of the code repository. if you go this route probably makes sense to have a parent docker container for more general system level details and a child container for setup specific to your code.
I believe the simpler workaround would be to change the 'context' itself.
So, for example, instead of giving:
docker build -t hello-demo-app .
which sets the current directory as the context, let's say you wanted the parent directory as the context, just use:
docker build -t hello-demo-app ..
You can also create a tarball of what the image needs first and use that as your context.
https://docs.docker.com/engine/reference/commandline/build/#/tarball-contexts
This behavior is given by the context directory that the docker or podman uses to present the files to the build process.
A nice trick here is by changing the context dir during the building instruction to the full path of the directory, that you want to expose to the daemon.
e.g:
docker build -t imageName:tag -f /path/to/the/Dockerfile /mysrc/path
using /mysrc/path instead of .(current directory), you'll be using that directory as a context, so any files under it can be seen by the build process.
This example you'll be exposing the entire /mysrc/path tree to the docker daemon.
When using this with docker the user ID who triggered the build must have recursively read permissions to any single directory or file from the context dir.
This can be useful in cases where you have the /home/user/myCoolProject/Dockerfile but want to bring to this container build context, files that aren't in the same directory.
Here is an example of building using context dir, but this time using podman instead of docker.
Lets take as example, having inside your Dockerfile a COPY or ADDinstruction which is copying files from a directory outside of your project, like:
FROM myImage:tag
...
...
COPY /opt/externalFile ./
ADD /home/user/AnotherProject/anotherExternalFile ./
...
In order to build this, with a container file located in the /home/user/myCoolProject/Dockerfile, just do something like:
cd /home/user/myCoolProject
podman build -t imageName:tag -f Dockefile /
Some known use cases to change the context dir, is when using a container as a toolchain for building your souce code.
e.g:
podman build --platform linux/s390x -t myimage:mytag -f ./Dockerfile /tmp/mysrc
or it can be a path relative, like:
podman build --platform linux/s390x -t myimage:mytag -f ./Dockerfile ../../
Another example using this time a global path:
FROM myImage:tag
...
...
COPY externalFile ./
ADD AnotherProject ./
...
Notice that now the full global path for the COPY and ADD is omitted in the Dockerfile command layers.
In this case the contex dir must be relative to where the files are, if both externalFile and AnotherProject are in /opt directory then the context dir for building it must be:
podman build -t imageName:tag -f ./Dockerfile /opt
Note when using COPY or ADD with context dir in docker:
The docker daemon will try to "stream" all the files visible on the context dir tree to the daemon, which can slowdown the build. And requires the user to have recursively permission from the context dir.
This behavior can be more costly specially when using the build through the API. However,with podman the build happens instantaneously, without needing recursively permissions, that's because podman does not enumerate the entire context dir, and doesn't use a client/server architecture as well.
The build for such cases can be way more interesting to use podman instead of docker, when you face such issues using a different context dir.
Some references:
https://docs.docker.com/engine/reference/commandline/build/
https://docs.podman.io/en/latest/markdown/podman-build.1.html
As is described in this GitHub issue the build actually happens in /tmp/docker-12345, so a relative path like ../relative-add/some-file is relative to /tmp/docker-12345. It would thus search for /tmp/relative-add/some-file, which is also shown in the error message.*
It is not allowed to include files from outside the build directory, so this results in the "Forbidden path" message."
Using docker-compose, I accomplished this by creating a service that mounts the volumes that I need and committing the image of the container. Then, in the subsequent service, I rely on the previously committed image, which has all of the data stored at mounted locations. You will then have have to copy these files to their ultimate destination, as host mounted directories do not get committed when running a docker commit command
You don't have to use docker-compose to accomplish this, but it makes life a bit easier
# docker-compose.yml
version: '3'
services:
stage:
image: alpine
volumes:
- /host/machine/path:/tmp/container/path
command: bash -c "cp -r /tmp/container/path /final/container/path"
setup:
image: stage
# setup.sh
# Start "stage" service
docker-compose up stage
# Commit changes to an image named "stage"
docker commit $(docker-compose ps -q stage) stage
# Start setup service off of stage image
docker-compose up setup
Create a wrapper docker build shell script that grabs the file then calls docker build then removes the file.
a simple solution not mentioned anywhere here from my quick skim:
have a wrapper script called docker_build.sh
have it create tarballs, copy large files to the current working directory
call docker build
clean up the tarballs, large files, etc
this solution is good because (1.) it doesn't have the security hole from copying in your SSH private key (2.) another solution uses sudo bind so that has another security hole there because it requires root permission to do bind.
I think as of earlier this year a feature was added in buildx to do just this.
If you have dockerfile 1.4+ and buildx 0.8+ you can do something like this
docker buildx build --build-context othersource= ../something/something .
Then in your docker file you can use the from command to add the context
ADD –from=othersource . /stuff
See this related post https://www.docker.com/blog/dockerfiles-now-support-multiple-build-contexts/
Workaround with links:
ln path/to/file/outside/context/file_to_copy ./file_to_copy
On Dockerfile, simply:
COPY file_to_copy /path/to/file
I was personally confused by some answers, so decided to explain it simply.
You should pass the context, you have specified in Dockerfile, to docker when
want to create image.
I always select root of project as the context in Dockerfile.
so for example if you use COPY command like COPY . .
first dot(.) is the context and second dot(.) is container working directory
Assuming the context is project root, dot(.) , and code structure is like this
sample-project/
docker/
Dockerfile
If you want to build image
and your path (the path you run the docker build command) is /full-path/sample-project/,
you should do this
docker build -f docker/Dockerfile .
and if your path is /full-path/sample-project/docker/,
you should do this
docker build -f Dockerfile ../
An easy workaround might be to simply mount the volume (using the -v or --mount flag) to the container when you run it and access the files that way.
example:
docker run -v /path/to/file/on/host:/desired/path/to/file/in/container/ image_name
for more see: https://docs.docker.com/storage/volumes/
I had this same issue with a project and some data files that I wasn't able to move inside the repo context for HIPAA reasons. I ended up using 2 Dockerfiles. One builds the main application without the stuff I needed outside the container and publishes that to internal repo. Then a second dockerfile pulls that image and adds the data and creates a new image which is then deployed and never stored anywhere. Not ideal, but it worked for my purposes of keeping sensitive information out of the repo.
In my case, my Dockerfile is written like a template containing placeholders which I'm replacing with real value using my configuration file.
So I couldn't specify this file directly but pipe it into the docker build like this:
sed "s/%email_address%/$EMAIL_ADDRESS/;" ./Dockerfile | docker build -t katzda/bookings:latest . -f -;
But because of the pipe, the COPY command didn't work. But the above way solves it by -f - (explicitly saying file not provided). Doing only - without the -f flag, the context AND the Dockerfile are not provided which is a caveat.
How to share typescript code between two Dockerfiles
I had this same problem, but for sharing files between two typescript projects. Some of the other answers didn't work for me because I needed to preserve the relative import paths between the shared code. I solved it by organizing my code like this:
api/
Dockerfile
src/
models/
index.ts
frontend/
Dockerfile
src/
models/
index.ts
shared/
model1.ts
model2.ts
index.ts
.dockerignore
Note: After extracting the shared code into that top folder, I avoided needing to update the import paths because I updated api/models/index.ts and frontend/models/index.ts to export from shared: (eg export * from '../../../shared)
Since the build context is now one directory higher, I had to make a few additional changes:
Update the build command to use the new context:
docker build -f Dockerfile .. (two dots instead of one)
Use a single .dockerignore at the top level to exclude all node_modules. (eg **/node_modules/**)
Prefix the Dockerfile COPY commands with api/ or frontend/
Copy shared (in addition to api/src or frontend/src)
WORKDIR /usr/src/app
COPY api/package*.json ./ <---- Prefix with api/
RUN npm ci
COPY api/src api/ts*.json ./ <---- Prefix with api/
COPY shared usr/src/shared <---- ADDED
RUN npm run build
This was the easiest way I could send everything to docker, while preserving the relative import paths in both projects. The tricky (annoying) part was all the changes/consequences caused by the build context being up one directory.
One quick and dirty way is to set the build context up as many levels as you need - but this can have consequences.
If you're working in a microservices architecture that looks like this:
./Code/Repo1
./Code/Repo2
...
You can set the build context to the parent Code directory and then access everything, but it turns out that with a large number of repositories, this can result in the build taking a long time.
An example situation could be that another team maintains a database schema in Repo1 and your team's code in Repo2 depends on this. You want to dockerise this dependency with some of your own seed data without worrying about schema changes or polluting the other team's repository (depending on what the changes are you may still have to change your seed data scripts of course)
The second approach is hacky but gets around the issue of long builds:
Create a sh (or ps1) script in ./Code/Repo2 to copy the files you need and invoke the docker commands you want, for example:
#!/bin/bash
rm -r ./db/schema
mkdir ./db/schema
cp -r ../Repo1/db/schema ./db/schema
docker-compose -f docker-compose.yml down
docker container prune -f
docker-compose -f docker-compose.yml up --build
In the docker-compose file, simply set the context as Repo2 root and use the content of the ./db/schema directory in your dockerfile without worrying about the path.
Bear in mind that you will run the risk of accidentally committing this directory to source control, but scripting cleanup actions should be easy enough.
I use docker-compose for a simple keycloak container and I've been trying to install a new theme for keycloak.
However I've been unable to copy even a single file to the container usnig a Dockerfile. The Dockerfile and docker-compose.yml are in the same directory
Neither of these commands work or cause any events or warnings in the logs.
COPY test /tmp/
COPY /home/adm/workspace/docker/keycloak-cluster/docker/kctheme/theme/login/. /opt/jboss/keycloak/themes/keycloak/login/
Copying manually with
sudo docker cp test docker_keycloak_1:/tmp
works without any issues.
Quick understanding on Docker.
docker build: Create an image from a Dockerfile
docker run: Create a container from an image.
(you can create yourself the image or use a existing image from docker hub )
Based on what you said, you have 2 options.
Create a new docker image based on the existing one and add the theme.
something like
# Dockerfile
FROM jboss/keycloak
COPY test /tmp/
COPY /home/adm/workspace/docker/keycloak-cluster/docker/kctheme/theme/login/. /opt/jboss/keycloak/themes/keycloak/login/
and then use docker build to create your new image
Volume the theme in the correct directory
using docker-compose volume
version: '3'
services:
keycloak:
image: quay.io/keycloak/keycloak:latest
volumes:
- "./docker/kctheme/theme/login:/opt/jboss/keycloak/themes/keycloak/login"
Files have to be in the same directory or a subdirectory of the directory with your Dockerfile build file if you use COPY, and have to be present at build time. No absolute paths.
/tmp as destination is also a bit tricky, because the startup process of the container might have a /tmp cleanout, which means that you would never see that file in a running container.