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https://github.com/freegroup/kube-s3

Kubernetes pods used shared S3 storage
https://github.com/freegroup/kube-s3

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Kubernetes pods used shared S3 storage

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## Shared storage with S3 backend

The storage is definitely the most complex and important part of an application setup, once this part is 

completed, 80% of the tasks are completed.



Mounting an S3 bucket into a pod using FUSE allows you to access the data as if it were on the local disk. The 

mount is a pointer to an S3 location, so the data is never synced locally. Once mounted, any pod can read or even write

from that directory without the need for explicit keys.



However, it can be used to import and parse large amounts of data into a database.



## Overview



![s3-mount](/images/s3-mount.png)



## Limitations

Generally S3 cannot offer the same performance or semantics as a local file system. More specifically:



 - random writes or appends to files require rewriting the entire file

 - metadata operations such as listing directories have poor performance due to network latency

 - eventual consistency can temporarily yield stale data(Amazon S3 Data Consistency Model)

 - no atomic renames of files or directories

 - no coordination between multiple clients mounting the same bucket

 - no hard links



## Before you Begin

You need to have a Kubernetes cluster, and the kubectl command-line tool must be configured to communicate with 

your cluster. If you do not already have a cluster, you can create one by using the [Gardener](https://gardener.cloud/).



Ensure that you have create the "imagePullSecret" in your cluster.

```sh 

kubectl create secret docker-registry artifactory --docker-server=.docker.repositories.sap.ondemand.com --docker-username= --docker-password= --docker-email= -n 

```



## Build and deploy

Change the settings in the `build.sh` file with your docker registry settings. 



```sh

#!/usr/bin/env bash



########################################################################################################################

# PREREQUISTITS

########################################################################################################################

#

# - ensure that you have a valid Artifactory or other Docker registry account

# - Create your image pull secret in your namespace

#   kubectl create secret docker-registry artifactory --docker-server=.docker.repositories.sap.ondemand.com --docker-username= --docker-password= --docker-email= -n 

# - change the settings below arcording your settings

#

# usage:

# Call this script with the version to build and push to the registry. After build/push the

# yaml/* files are deployed into your cluster

#

#  ./build.sh 1.0

#

VERSION=$1

PROJECT=kube-s3

REPOSITORY=cp-enablement.docker.repositories.sap.ondemand.com



# causes the shell to exit if any subcommand or pipeline returns a non-zero status.

set -e

# set debug mode

#set -x



.

.

.

.



```

Create the S3Fuse Pod and check the status:



```sh

# build and push the image to your docker registry

./build.sh 1.0 



# check that the pods are up and running

kubectl get pods



```



## Check success

Create a demo Pod and check the status:

```sh 

kubectl apply -f ./yaml/example_pod.yaml



# wait some second to get the pod up and running...

kubectl get pods



# go into the pd and check that the /var/s3 is mounted with your S3 bucket content inside

kubectl exec -ti test-pd  sh



# inside the pod

ls -la /var/s3



```



## Why does this work?

Containerd (and previously docker) allows containers to share the host mount namespace. This feature makes 

it possible to mount a s3fs container file system to a host file system through a shared mount, providing a persistent

network storage with S3 backend.



The key part is 



```

mountPath: /var/s3

mountPropagation: Bidirectional

```



which enables the volume to be mounted as shared inside the pod. When the container starts. it will mount the S3 bucket

onto `/var/s3` and consequently the data will be available under `/mnt/data-s3fs` on the host and thus to any other 

container/pod running on it (and has `/mnt/data-s3fs` mounted too).