To demonstrate transferring files to and from a running container we first need to deploy an application. To do this run the command:

oc new-app openshiftkatacoda/blog-django-py --name blog

So that we can access it from a web browser, we also need to expose it by creating a Route.

oc expose service/blog

To monitor the deployment of the application run:

oc rollout status deployment/blog

The command will exit once the deployment has completed and the web application is ready.

The result of the deployment will be the running container. You can see the name of the pods corresponding to the running containers for this application, by running:

oc get pods --selector deployment=blog

You only have one instance of the application so only one pod will be listed, similar to:

NAME                    READY   STATUS    RESTARTS   AGE
blog-5dc99d7545-rkvzt   1/1     Running   0          1m12s

For subsequent commands which need to interact with that pod, you will need to use the name of the pod, as an argument.

To make it easier to reference the name of the pod in these instructions, we define here a shell function to capture the name so it can be stored in an environment variable. That environment variable will then be used in the commands you run.

The command we will run from the shell function to get out just the name of the pod will be:

oc get pods --selector deployment=blog -o jsonpath='{.items[?(@.status.phase=="Running")].metadata.name}'

As above this uses oc get pods with a label selector, but we also use a jsonpath query to extract the name of the running pod.

To create the shell function run:

pod() { local selector=$1; local query='?(@.status.phase=="Running")'; oc get pods --selector $selector -o jsonpath="{.items[$query].metadata.name}"; }

To capture the name of the pod for this application in the POD environment variable, run:

POD=`pod deployment=blog`; echo $POD

To create an interactive shell within the same container running the application, you can use the oc rsh command, supplying it the environment variable holding the name of the pod.

oc rsh $POD

From within the interactive shell, see what files exist in the application directory.

ls -las

This will yield output similar to:

total 80
 0 drwxrwxr-x. 1 default    root    52 Oct 24 02:51 .
 0 drwxrwxr-x. 1 default    root    28 Jun 18 02:10 ..
 4 -rwxrwxr-x. 1 default    root  1454 Jun 18 02:07 app.sh
 0 drwxrwxr-x. 1 default    root    43 Jun 18 02:11 blog
 0 drwxrwxr-x. 2 default    root    25 Jun 18 02:07 configs
 4 -rw-rw-r--. 1 default    root   230 Jun 18 02:07 cronjobs.py
44 -rw-r--r--. 1 1000520000 root 44032 Oct 24 02:51 db.sqlite3
 4 -rw-rw-r--. 1 default    root   430 Jun 18 02:07 Dockerfile
 0 drwxrwxr-x. 2 default    root    25 Jun 18 02:07 htdocs
 0 drwxrwxr-x. 1 default    root    25 Jun 18 02:11 katacoda
 4 -rwxrwxr-x. 1 default    root   806 Jun 18 02:07 manage.py
 0 drwxrwxr-x. 3 default    root    20 Jun 18 02:11 media
 0 drwxrwxr-x. 1 default    root    19 Apr  3  2019 .pki
 4 -rw-rw-r--. 1 default    root   832 Jun 18 02:07 posts.json
 8 -rw-rw-r--. 1 default    root  7861 Jun 18 02:07 README.md
 4 -rw-rw-r--. 1 default    root   203 Jun 18 02:07 requirements.txt
 4 -rw-rw----. 1 default    root  1024 Apr  3  2019 .rnd
 0 drwxrwxr-x. 4 default    root    57 Jun 18 02:09 .s2i
 0 drwxrwxr-x. 4 default    root    30 Jun 18 02:11 static
 0 drwxrwxr-x. 2 default    root   148 Jun 18 02:07 templates

For the application being used, this has created a database file:

44 -rw-r--r--. 1 1000520000 root 44032 Oct 24 02:51 db.sqlite3

Lets look at how this database file can be copied back to the local machine.

To confirm what directory the file is located in, inside of the container, run:

pwd

This should display:

/opt/app-root/src

To exit the interactive shell and return to the local machine run:

exit

To copy files from the container to the local machine the oc rsync command can be used.

The form of the command when copying a single file from the container to the local machine is:

oc rsync <pod-name>:/remote/dir/filename ./local/dir

To copy the single database file run:

oc rsync $POD:/opt/app-root/src/db.sqlite3 .

This should display output similar to:

receiving incremental file list
db.sqlite3

sent 43 bytes  received 44,129 bytes  88,344.00 bytes/sec
total size is 44,032  speedup is 1.00

Check the contents of the current directory by running:

ls -las

and you should see that the local machine now has a copy of the file.

44 -rw-r--r--  1 root root 44032 Oct 24 04:15 db.sqlite3

Note that the local directory into which you want the file copied must exist. If you didn't want to copy it into the current directory, ensure the target directory has been created beforehand.

In addition to copying a single file, a directory can also be copied. The form of the command when copying a directory to the local machine is:

oc rsync <pod-name>:/remote/dir ./local/dir

To copy the media directory from the container, run:

oc rsync $POD:/opt/app-root/src/media .

If you wanted to rename the directory when it is being copied, you should create the target directory with the name you want to use first.

mkdir uploads

and then to copy the files use the command:

oc rsync $POD:/opt/app-root/src/media/. uploads

To ensure only the contents of the directory on the container are copied, and not the directory itself, the remote directory is suffixed with /..

Note that if the target directory contains existing files with the same name as a file in the container, the local file will be overwritten. If there are additional files in the target directory which don't exist in the container, those files will be left as is. If you did want an exact copy, where the target directory was always updated to be exactly the same as what exists in the container, use the --delete option to oc rsync.

When copying a directory, you can be more selective about what is copied by using the --exclude and --include options to specify patterns to be matched against directories and files, with them being excluded or included as appropriate.

If there is more than one container running within a pod, you will need to specify which container you want to work with by using the --container option.

To copy files from the local machine to the container, the oc rsync command is again used.

The form of the command when copying files from the local machine to the container is:

oc rsync ./local/dir <pod-name>:/remote/dir

Unlike when copying from the container to the local machine, there is no form for copying a single file. To copy selected files only, you will need to use the --exclude and --include options to filter what is and isn't copied from a specified directory.

To illustrate the process for copying a single file, consider the case where you had deployed a web site and had not included a robots.txt file, but needed to quickly stop a web robot which was crawling your site.

A request to fetch the current robots.txt file for the web site fails with a HTTP 404 Not Found response.

curl --head http://blog-myproject.[[HOST_SUBDOMAIN]]-80-[[KATACODA_HOST]].environments.katacoda.com/robots.txt

Create a robots.txt file to upload.

cat > robots.txt << ! User-agent: * Disallow: / !

For the web application being used, it hosts static files out of the htdocs sub directory of the application source code. To upload the robots.txt file run:

oc rsync . $POD:/opt/app-root/src/htdocs --exclude=* --include=robots.txt --no-perms

As already noted it is not possible to copy a single file, so we indicate that the current directory should be copied, but use the --exclude=* option to first say that all files should be ignored when performing the copy. That pattern is then overridden for just the robots.txt file by using the --include=robots.txt file, ensuring the robots.txt file is copied.

When copying files to the container, it is required that the directory into which files are being copied exists, and that it is writable to the user or group that the container is being run as. Permissions on directories and files should be set as part of the process of building the image.

In the above command, the --no-perms option is also used because the target directory in the container, although writable by the group the container is run as, is owned by a different user to that which the container is run as. This means that although files can be added to the directory, permissions on existing directories cannot be changed. The --no-perms options tells oc rsync to not attempt to update permissions to avoid it failing and returning errors.

Having uploaded the robots.txt file, fetching the robots.txt file again now succeeds.

curl http://blog-myproject.[[HOST_SUBDOMAIN]]-80-[[KATACODA_HOST]].environments.katacoda.com/robots.txt

This worked without needing to take any further actions as the Apache HTTPD server being used to host static files, would automatically detect the presence of a new file in the directory.

If instead of copying a single file you wanted to copy a complete directory, leave off the --include and --exclude options. To copy the complete contents of the current directory to the htdocs directory in the container, run:

oc rsync . $POD:/opt/app-root/src/htdocs --no-perms

Just be aware that this will be everything, including notionally hidden files or directories starting with ".". You should therefore be careful, and if necessary be more specific by using --include or --exclude options to limit the set of files or directories copied.

In addition to being able to manually upload or download files when you choose to, the oc rsync command can also be set up to perform live synchronization of files between your local computer and the container.

That is, the file system of your local computer will be monitored for any changes made to files. When there is a change to a file, the changed file will be automatically copied up to the container.

This same process can also be run in the opposite direction if required, with changes made in the container being automatically copied back to your local computer.

An example of where it can be useful to have changes automatically copied from your local computer into the container is during the development of an application.

For scripted programming languages such as PHP, Python or Ruby, where no separate compilation phase is required, provided that the web server can be manually restarted without causing the container to exit, or if the web server always reloads code files which have been modified, you can perform live code development with your application running inside of OpenShift.

To demonstrate this ability, clone the Git repository for the web application which you have already deployed.

git clone https://github.com/openshift-katacoda/blog-django-py

This will create a sub directory blog-django-py containing the source code for the application:

Cloning into 'blog-django-py'...
remote: Enumerating objects: 3, done.
remote: Counting objects: 100% (3/3), done.
remote: Compressing objects: 100% (3/3), done.
remote: Total 412 (delta 0), reused 0 (delta 0), pack-reused 409
Receiving objects: 100% (412/412), 68.49 KiB | 701.00 KiB/s, done.
Resolving deltas: 100% (200/200), done.

Now run the following command to have oc rsync perform live synchronisation of the code, copying any changes from the blog-django-py directory up to the container.

oc rsync blog-django-py/. $POD:/opt/app-root/src --no-perms --watch &

In this case we are running this as a background process as we only have the one terminal window available, you could run it as a foreground process in a separate terminal if doing this yourself.

You can see the details for the background process by running:

jobs

When you initially ran this oc rsync command, you will see that it copied up the files so the local and remote directory are synchronized. Any changes made to the local files will now be automatically copied up to the remote directory.

Before we make a change, bring up the web application we have deployed in a separate browser window by using the URL:

http://blog-myproject.[[HOST_SUBDOMAIN]]-80-[[KATACODA_HOST]].environments.katacoda.com/

You should see that the color of the title banner for the web site is red.

Lets change that banner color by running the command:

echo "BLOG_BANNER_COLOR = 'blue'" >> blog-django-py/blog/context_processors.py

Wait to see that the changed file is uploaded, and then refresh the page for the web site.

Unfortunately you will see that the title banner is still red. This is because for Python any code changes are cached by the running process and it is necessary to restart the web server application processes.

For this deployment the WSGI server mod_wsgi-express is being used. To trigger a restart of the web server application processes, run:

oc rsh $POD kill -HUP 1

This command will have the affect of sending a HUP signal to process ID 1 running within the container, which is the instance of mod_wsgi-express which is running. This will trigger the required restart and reloading of the application, but without the web server actually exiting.

Refresh the page for the web site once more and the title banner should now be blue.

Note that the name of the pod as displayed in the title banner is unchanged, indicating that the pod was not restarted and only the web server application processes were restarted.

Manually forcing a restart of the web server application processes will get the job done, but a better way is if the web server can automatically detect code changes and trigger a restart.

In the case of mod_wsgi-express and how this web application has been configured, this can be enabled by setting an environment variable for the deployment. To set this environment variable run:

oc set env deployment/blog MOD_WSGI_RELOAD_ON_CHANGES=1

This command will update the deployment configuration, shutdown the existing pod and replace it with a new instance of our application with the environment variable now being passed through to the application.

Monitor the re-deployment of the application by running:

oc rollout status deployment/blog

Because the existing pod has been shutdown, we will need to capture again the new name for the pod.

POD=`pod deployment=blog`; echo $POD

You may also notice that the synchronization process we had running in the background may have stopped. This is because the pod it was connected to had been shutdown.

You can check this is the case by running:

jobs

If it is still showing as running, due to shutdown of the pod not yet having been detected, run the following command to kill it:

kill -9 %1

Ensure the background task has exited:

jobs

Now run the oc rsync command again, against the new pod.

oc rsync blog-django-py/. $POD:/opt/app-root/src --no-perms --watch &

Refresh the page for the web site again and the title banner should still be blue, but you will notice that the pod name displayed has changed.

Modify the code file once more, setting the color to green.

echo "BLOG_BANNER_COLOR = 'green'" >> blog-django-py/blog/context_processors.py

Refresh the web site page again, multiple times if need be, until the title banner shows as green. The change may not be immediate as the file synchronization may take a few moments, as may the detection of the code changes and restart of the web server application process.

Kill the synchronization task by running:

kill -9 %1

Although one can synchronize files from the local computer into a container in this way, whether you can use it as a mechanism for enabling live coding will depend on the programming language being used, and the web application stack being used. This was possible for Python when using mod_wsgi-express, but may not be possible with other WSGI servers for Python, or other programming languages.

Do note that even for the case of Python, this can only be used where modifying code files. If you need to install additional Python packages, you would need to re-build the application from the original source code. This is because changes to packages required, which for Python is given in the requirements.txt file, isn't going to trigger the installation of that package when using this mechanism.

If you are mounting a persistent volume into the container for your application and you need to copy files into it, then oc rsync can be used in the same way as described previously to upload files. All you need to do is supply as the target directory, the path of where the persistent volume is mounted in the container.

If you haven't as yet deployed your application, but are wanting to prepare in advance a persistent volume with all the data it needs to contain, you can still claim a persistent volume and upload the data to it. In order to do this, you will though need to deploy a dummy application against which the persistent volume can be mounted.

To create a dummy application for this purpose run the command:

oc new-app centos/httpd-24-centos7 --name dummy

We are using the Apache HTTPD server purely as a means of keeping the pod running, as well as creating a deployment configuration.

To monitor the startup of the pod and ensure it is deployed, run:

oc rollout status deployment/dummy

Now that we have a running application, we next need to claim a persistent volume and mount it against our dummy application. When doing this we assign it a claim name of data so we can refer to the claim by a set name later on. We mount the persistent volume at /mnt inside of the container, the traditional directory used in Linux systems for temporarily mounting a volume.

oc set volume deployment/dummy --add --name=tmp-mount --claim-name=data --type pvc --claim-size=1G --mount-path /mnt

This will cause a new deployment of our dummy application, this time with the persistent volume mounted. Again monitor the progress of the deployment so we know when it is complete, by running:

oc rollout status deployment/dummy

To confirm that the persistent volume claim was successful, you can run:

oc get pvc

With the dummy application now running, and with the persistent volume mounted, capture the name of the pod for the running application.

POD=`pod deployment=dummy`; echo $POD

We can now copy any files into the persistent volume, using the /mnt directory where we mounted the persistent volume, as the target directory. In this case since we are doing a one off copy, we can use the tar strategy instead of the rsync strategy.

oc rsync ./ $POD:/mnt --strategy=tar

When complete, you can validate that the files were transferred by listing the contents of the target directory inside of the container.

oc rsh $POD ls -las /mnt

If you were done with this persistent volume and perhaps needed to repeat the process with another persistent volume and with different data, you can unmount the persistent volume but retain the dummy application.

oc set volume deployment/dummy --remove --name=tmp-mount

Monitor the process once again to confirm the re-deployment has completed.

oc rollout status deployment/dummy

Capture the name of the current pod again:

POD=`pod deployment=dummy`; echo $POD

and look again at what is in the target directory. It should be empty at this point. This is because the persistent volume is no longer mounted and you are looking at the directory within the local container file system.

oc rsh $POD ls -las /mnt

If you already have an existing persistent volume claim, as we now do, you could mount the existing claimed volume against the dummy application instead. This is different to above where we both claimed a new persistent volume and mounted it to the application at the same time.

oc set volume deployment/dummy --add --name=tmp-mount --claim-name=data --mount-path /mnt

Look for completion of the re-deployment:

oc rollout status deployment/dummy

Capture the name of the pod:

POD=`pod deployment=dummy`; echo $POD

and check the contents of the target directory. The files we copied to the persistent volume should again be visible.

oc rsh $POD ls -las /mnt

When done and you want to delete the dummy application, use oc delete to delete it, using a label selector of deployment=dummy to ensure we only delete the resource objects related to the dummy application.

oc delete all --selector deployment=dummy

Check that all the resource objects have been deleted.

oc get all --selector deployment=dummy -o name

Although we have deleted the dummy application, the persistent volume claim still exists and can later be mounted against your actual application to which the data belongs.

oc get pvc