How to perform automatic data copy/reset with Kubernetes ?

[Pierrick]

Hi.

Here's what I'm trying to set up :

 * An app which handle files, let's say profile pictures. A volume mount is used.

 * A single staging environment. The app is not yet in production.

 * A CD pipeline with Jenkins, to automatically  apply updated k8s configuration (with new docker image verions of the app).

 * A way to copy some profile pictures versionned with git on the volume mount. Those pictures are copied in the app image (Dockerfile) during the CD step.

The goal is to reset (or reload) the mount with the versionned pictures in git, everytime a commit is done on the staging branch.

My question is about the last point :

 * how can I trigger the copy ?

 * should I use a job ?

 * should I use a multiple read-write consumer volume type (e.g flocker) ?

[Brandon Philips]

On Thu, Sep 15, 2016 at 3:47 AM Pierrick <pdo...@gmail.com> wrote:

Hi.

Here's what I'm trying to set up :

 * An app which handle files, let's say profile pictures. A volume mount is used.

 * A single staging environment. The app is not yet in production.

 * A CD pipeline with Jenkins, to automatically  apply updated k8s configuration (with new docker image verions of the app).

 * A way to copy some profile pictures versionned with git on the volume mount. Those pictures are copied in the app image (Dockerfile) during the CD step.

Instead of bundling the app with the images you could use a gitRepo volume and have the directory directly populated: http://kubernetes.io/docs/user-guide/volumes/#gitrepo

 

The goal is to reset (or reload) the mount with the versionned pictures in git, everytime a commit is done on the staging branch.

My question is about the last point :

 * how can I trigger the copy ?

 * should I use a job ?

I would create a container that polls or listens to git webhooks and updates the gitRepo volume. Then it would roll the application deployment once the volume was updated.

There isn't an off the shelf chunk of code that will do this for you unfortunately. You would need to string it together with some poll/webhook code and the Kubernetes client or API.

Another, potentially easier, way to tackle this would be to create a container and schedule it in the same pod in your app. The container would simply have a git client inside of it and execute a bash script that does a pull on some interval:

`while true; do git clone https://git.repo/photos.git photos; git pull https://git.repo/photos.git staging; sleep 10; done`

Hope that helps! Let us know what you come up with!

Cheers,

Brandon

[Derek Mahar]

On Thursday, 15 September 2016 08:51:47 UTC-4, Brandon Philips wrote:

Instead of bundling the app with the images you could use a gitRepo volume and have the directory directly populated: http://kubernetes.io/docs/user-guide/volumes/#gitrepo

When does the gitRepo volume clone the Git repository?  In the case where cluster nodes have no access to the Internet or any other host outside the cluster (or the cluster shouldn't make any external connections), is it possible to clone the Git repository before the volume is created or mounted?

I would create a container that polls or listens to git webhooks and updates the gitRepo volume. Then it would roll the application deployment once the volume was updated.

There isn't an off the shelf chunk of code that will do this for you unfortunately. You would need to string it together with some poll/webhook code and the Kubernetes client or API.

How does a container update the gitRepo volume?  Is the volume a standard Git repository and workspace?

Another, potentially easier, way to tackle this would be to create a container and schedule it in the same pod in your app. The container would simply have a git client inside of it and execute a bash script that does a pull on some interval:

`while true; do git clone https://git.repo/photos.git photos; git pull https://git.repo/photos.git staging; sleep 10; done`

How would this differ from a gitRepo volume?

Derek

[Derek Mahar]

On Thursday, 15 September 2016 08:51:47 UTC-4, Brandon Philips wrote:

Instead of bundling the app with the images you could use a gitRepo volume and have the directory directly populated: http://kubernetes.io/docs/user-guide/volumes/#gitrepo

Is it also possible to use a Git repository from an SSH source and specify a private key and optional secret?  The only example in the documentation shows a repository URL that uses the git protocol.

Derek

[Pierrick]

I would create a container that polls or listens to git webhooks and updates the gitRepo volume. Then it would roll the application deployment once the volume was updated.

Interesting. The pictures are already checked out from git during the jenkins build (same repo as my app). I'd prefer not relying on git somewhere else in the cluster.

 

There isn't an off the shelf chunk of code that will do this for you unfortunately. You would need to string it together with some poll/webhook code and the Kubernetes client or API.

Right. For now, I'll try to make it simple :

 * one replica for my app pod

 * one google persistent volume for the pictures, mounted in the app pod

 * after each roll out, I'll manually run a command in the app container to perform the copy (from app/fixtures/*.jpg to /my-volume/pictures)

Later, I'm wondering if something more sophisticated (but resilient/efficient) can be possible : 

 * possibly several replicas of my app pod

 * a flocker-based volume mount

 * a jenkins job, lauchable on demand to command the copy

How does that sound ?

Cheers,