I am learning about Volumes in the Kubernetes.
I understood the concept of Volume and types of volume.
But, I am confused about the mouthPath property. Following my YAML file:
apiVersion: v1
kind: Pod
metadata:
name: nginx-alpine-volume
spec:
containers:
- name: nginx
image: nginx:alpine
volumeMounts:
- name: html
mountPath: /usr/share/nginx/html
readOnly: true
resources:
- name: html-updater
image: alpine
command: ["/bin/sh", "-c"]
args:
- while true; do date >> /mohit/index.html;sleep 10; done
resources:
volumeMounts:
- name: html
mountPath: /mohit
volumes:
- name: html
emptyDir: {}
Question: What is the use of the mountPath property. Here, I am using one pod with two containers. Both containers have different mounPath values.
Update:
Consider the mount path as the directory where you are attaching or mounting the files or system
While your actual volume is emptyDir
What basically the idea is there to both container have different mount path
as both containers need to use different folders
While as your volume is single name html so locally from volume both container pointing or using the different folders
both containers manage the different files at their mounting point (or folder)
so mount path is a point or directly where your container will be managing files.
Empty dir : https://kubernetes.io/docs/concepts/storage/volumes/#emptydir
Read more at : https://kubernetes.io/docs/tasks/access-application-cluster/communicate-containers-same-pod-shared-volume/
if you see this example: https://github.com/harsh4870/Kubernetes-wordpress-php-fpm-nginx/blob/master/wordpress-deployment.yaml
it has the same two containers with mount path and emptydir volume
what i am doing is attaching the Nginx configuration file, to the container so Nginx will use that configuration file which i am mounting from outside to the container.
My config file stored inside configmap or secret.
Related
In my k8s pod, I want to give a container access to a S3 bucket, mounted with rclone.
Now, the container running rclone needs to run with --privileged, which is a problem for me, since my main-container will run user code which I have no control of and can be potentially harmful to my Pod.
The solution I’m trying now is to have a sidecar-container just for the task of running rclone, mounting S3 in a /shared_storage folder, and sharing this folder with the main-container through a Volume shared-storage. This is a simplified pod.yml file:
apiVersion: v1
kind: Pod
metadata:
name: two-containers
spec:
restartPolicy: Never
volumes:
- name: shared-storage
emptyDir: {}
containers:
- name: main-container
image: busybox
command: ["sh", "-c", "sleep 1h"]
volumeMounts:
- name: shared-storage
mountPath: /shared_storage
# mountPropagation: HostToContainer
- name: sidecar-container
image: mycustomsidecarimage
securityContext:
privileged: true
command: ["/bin/bash"]
args: ["-c", "python mount_source.py"]
env:
- name: credentials
value: XXXXXXXXXXX
volumeMounts:
- name: shared-storage
mountPath: /shared_storage
mountPropagation: Bidirectional
The pod runs fine and from sidecar-container I can read, create and delete files from my S3 bucket.
But from main-container no files are listed inside of shared_storage. I can create files (if I set readOnly: false) but those do not appear in sidecar-container.
If I don’t run the rclone mount to that folder, the containers are able to share files again. So that tells me that is something about the rclone process not letting main-container read from it.
In mount_source.py I am running rclone with --allow-other and I have edit etc/fuse.conf as suggested here.
Does anyone have an idea on how to solve this problem?
I've managed to make it work by using:
mountPropagation: HostToContainer on main-container
mountPropagation: Bidirectional on sidecar-container
I can control read/write permissions to specific mounts using readOnly: true/false on main-container. This is of course also possible to set within rclone mount command.
Now the main-container does not need to run in privileged mode and my users code can have access to their s3 buckets through those mount points!
Interestingly, it doesn't seem to work if I set volumeMount:mountPath to be a sub-folder of the rclone mounted path. So if I want to grant main-container different read/write permissions to different subpaths, I had to create a separate rclone mount for each sub-folder.
I'm not 100% sure if there's any extra security concerns with that approach though.
I'm trying to create a new Kubernetes deployment that will allow me to persist a pod's state when it is restarted or shutdown. Just for some background, the Kubernetes instance is a managed Amazon EKS Cluster, and I am trying to incorporate an Amazon EFS-backed Persistent Volume that is mounted to the pod.
Unfortunately as I have it now, the PV mounts to /etc/ as desired, but the contents are nearly empty, except for some files that were modified during boot.
The deployment yaml looks as below:
kind: Deployment
apiVersion: apps/v1
spec:
replicas: 1
selector:
matchLabels:
app: testpod
template:
metadata:
creationTimestamp: null
labels:
app: testpod
spec:
volumes:
- name: efs
persistentVolumeClaim:
claimName: efs
containers:
- name: testpod
image: 'xxxxxxxxxxxx.dkr.ecr.us-east-2.amazonaws.com/testpod:latest'
args:
- /bin/init
ports:
- containerPort: 443
protocol: TCP
resources: {}
volumeMounts:
- name: efs
mountPath: /etc
subPath: etc
terminationMessagePath: /dev/termination-log
terminationMessagePolicy: File
imagePullPolicy: IfNotPresent
securityContext:
capabilities:
add:
- ALL
restartPolicy: Always
terminationGracePeriodSeconds: 60
dnsPolicy: ClusterFirst
securityContext: {}
schedulerName: default-scheduler
Any ideas of what could be going wrong? I would expect /etc/ to be populated with the contents of the image.
Edit:
This seems to be working fine in Docker by using the same image, creating a volume with docker volume create <name> and then mounting it as -v <name>:/etc.
Kubernetes does not have the Docker feature that populates volumes based on the contents of the image. If you create a new volume (whether an emptyDir volume or something based on cloud storage like AWS EBS or EFS) it will start off empty, and hide whatever was in the container.
As such, you can’t mount a volume over large parts of the container; it won’t work to mount a volume over your application’s source tree, or over /etc as you show. For files in /etc in particular, a better approach would be to use a Kubernetes ConfigMap to hold specific files you want to add to that directory. (Store your config files in source control and add them as part of the deployment sequence; don’t try to persist untracked modifications to deployed files.)
my guess would be the mounts in containers works exactly the same way as mounts in operating system.. if you mount something at /etc you simply overwrite (better word 'cover') what has been there before.. if you mount empty EFS there will be empty folder
I tried what you tried in docker and (surprise for me) it works the way you describe.. it's likely because docker volumes are simply technologically something else than kubernetes volume claims (especially backed by EFS) this explains it: Docker mount to folder overriding content
tldr: if docker volume is empty files will be mirrored
I don't personally think with k8s and EFS you can achieve what you're trying to
I think you might be interested in "nsfdsuds", potentially: it establishes an overlayfs for a Kubernetes container in which the writable, top layer of the overlayfs can be on a PersistentVolume of your choice.
https://github.com/Sha0/nsfdsuds
I have a pod which contains two containers. One container is a web application and another store some static data for this web application.
The data here is a set of files which are stored in the folder of this container with name /data and that's only function of the container to store this data and expose them to the web application.
I'm looking for the way to share the content of this folder with web application container in this pod.
If I'm using the YAML spec below the folder in both containers is empty. Is there a way to share the data from container folder without cleaning it up?
apiVersion: v1
kind: Pod
metadata:
name: my-pod
labels:
app: my-app
version: 1.2.3
spec:
volumes:
- name: my-app-data-volume
containers:
- name: my-app-server
image: my-app-server-container-name
volumeMounts:
- name: my-app-data-volume
mountPath: /data
ports:
- containerPort: 8080
- name: my-app-data
image: my-app-data-container-name
volumeMounts:
- name: my-app-data-volume
mountPath: /data
You can use an EmptyDir volume for this. Specify the container that contains the files as an initContainer, then copy the files into the EmptyDir volume. Finally, mount that volume in the web app container.
I have a Docker image and I'd like to share an entire directory on a volume (a Persistent Volume) on Kubernetes.
Dockerfile
FROM node:carbon
WORKDIR /node-test
COPY hello.md /node-test/hello.md
VOLUME /node-test
CMD ["tail", "-f", "/dev/null"]
Basically it copies a file hello.md and makes it part of the image (lets call it my-image).
On the Kubernetes deployment config I create a container from my-image and I share a specific directory to a volume.
Kubernetes deployment
# ...
spec:
containers:
- image: my-user/my-image:v0.0.1
name: node
volumeMounts:
- name: node-volume
mountPath: /node-test
volumes:
- name: node-volume
persistentVolumeClaim:
claimName: node-volume-claim
I'd expect to see the hello.md file in the directory of the persistent volume, but nothing shows up.
If I don't bind the container to a volume I can see the hello.md file (with kubectl exec -it my-container bash).
I'm not doing anything different from what this official Kubernetes example does. As matter of fact I can change mountPath and switch to the official Wordpress image and it works as expected.
How can Wordpress image copy all files into the volume directory?
What's in the Wordpress Dockerfile that is missing on mine?
In order not to overwrite the existing files/content, you can use subpath to mount the testdir directory (In the example below) in the existing Container file system.
volumeMounts:
- name: node-volume
mountPath: /node-test/testdir
subPath: testdir
volumes:
- name: node-volume
persistentVolumeClaim:
claimName: node-volume-claim
you can find for more information here using-subpath
UPDATE:
I connected to the minikubevm and I see my host directory mounted but there is no files there. Also when I create a file there it will not in my host machine. Any link are between them
I try to mount an host directory for developing my app with kubernetes.
As the doc recommended, I am using minikube for running my kubernetes cluster on my pc. The goal is to create a develop environment with docker and kubernetes for develop my app. I want to mount a local directory so my docker will read the code app from there. But it is not work. Any help would be really appreciate.
my test app (server.js):
var http = require('http');
var handleRequest = function(request, response) {
response.writeHead(200);
response.end("Hello World!");
}
var www = http.createServer(handleRequest);
www.listen(8080);
my Dockerfile:
FROM node:latest
WORKDIR /code
ADD code/ /code
EXPOSE 8080
CMD server.js
my pod kubernetes configuration: (pod-configuration.yaml)
apiVersion: v1
kind: Pod
metadata:
name: apiserver
spec:
containers:
- name: node
image: myusername/nodetest:v1
ports:
- containerPort: 8080
volumeMounts:
- name: api-server-code-files
mountPath: /code
volumes:
- name: api-server-code-files
hostPath:
path: /home/<myuser>/Projects/nodetest/api-server/code
my folder are:
/home/<myuser>/Projects/nodetest/
- pod-configuration.yaml
- api-server/
- Dockerfile
- code/
- server.js
When I running my docker image without the hostPath volume it is of course works but the problem is that on each change I will must recreate my image that is really not powerful for development, that's why I need the volume hostPath.
Any idea ? why i don't success to mount my local directory ?
Thanks for the help.
EDIT: Looks like the solution is to either use a privilaged container, or to manually mount your home folder to allow the MiniKube VM to read from your hostPath -- https://github.com/boot2docker/boot2docker#virtualbox-guest-additions. (Credit to Eliel for figuring this out).
It is absolutely possible to configure a hostPath volume with minikube - but there are a lot of quirks and there isn't very good support for this particular issue.
Try removing ADD code/ /code from your Dockerfile. Docker's "ADD" instruction is copying the code from your host machine into your container's /code directory. This is why rebuilding the image successfully updates your code.
When Kubernetes tries to mount the container's /code directory to the host path, it finds that this directory is already full of the code that was baked into the image. If you take this out of the build step, Kubernetes should be able to successfully mount the host path at runtime.
Also be sure to check the permissions of the code/ directory on your host machine.
My only other thought is related to mounting in the root directory. I had issues when mounting Kubernetes hostPath volumes to/from directories in the root directory (I assume this was permissions related). So, something else to try would be a mountPath like /var/www/html.
Here's an example of a functional hostPath volume:
apiVersion: v1
kind: Pod
metadata:
name: example
spec:
volumes:
- name: example-volume
hostPath:
path: '/Users/example-user/code'
containers:
- name: example-container
image: example-image
volumeMounts:
- mountPath: '/var/www/html'
name: example-volume
They have now given the minikube mount which works on all environment
https://github.com/kubernetes/minikube/blob/master/docs/host_folder_mount.md
Tried on Mac:
$ minikube mount ~/stuff/out:/mnt1/out
Mounting /Users/macuser/stuff/out into /mnt1/out on the minikube VM
This daemon process needs to stay alive for the mount to still be accessible...
ufs starting
And in pod:
apiVersion: v1
kind: Pod
metadata:
name: myServer
spec:
containers:
- name: myServer
image: myImage
volumeMounts:
- mountPath: /mnt1/out
name: volume
# Just spin & wait forever
command: [ "/bin/bash", "-c", "--" ]
args: [ "while true; do sleep 30; done;" ]
volumes:
- name: volume
hostPath:
path: /mnt1/out
Best practice would be building the code into your image, you should not run an image with code just coming from the disk. Your Dockerfile should look more like:
FROM node:latest
COPY /code/server.js /code/server.js
EXPOSE 8080
CMD /code/server.js
Then you run the Image on Kubernetes without any volumes. You need to rebuild the image and update the pod every time you update the code.
Also, I'm currently not aware that minikube allows for mounts between the VM it creates and the host you are running it on.
If you really want the extreme fast feedback cycle of changing code while the container is running, you might be able to use just Docker by itself with -v /path/to/host/code:/code without Kubernetes and then once you are ready build the image and deploy and test it on minikube. However, I'm not sure that would work if you're changing the main .js file of your node app.