add flexvolume background

Author: remkohdev-ibm

workshop/Lab5/cos-with-s3fs/README.md

@@ -6,7 +6,9 @@ This hands-on lab for object storage on Kubernetes is called `Add Object Storage
 
 `IBM Cloud Object Storage plugin` is a Kubernetes volume plugin that enables Kubernetes pods to access `IBM Cloud Object Storage` buckets. The plugin has two components: a dynamic provisioner and a FlexVolume driver for mounting the buckets using `s3fs-fuse` on a worker node.
 
-[`s3fs`](https://github.com/s3fs-fuse/s3fs-fuse) allows Linux and macOS to mount an S3 bucket via FUSE. If you want to learn more about `s3fs-fuse` and FUSE you can do the optional [s3fs lab](../fuse/README.md).
+`FlexVolume` is a so-called `out-of-tree` volume plugin, as is the `Container Storage Interface (CSI)`. `Out-of-tree` volume plugins enable storage developers to create custom storage plugins. For more information about `FlexVolume`, go to [flexvolume](../../flexvolume/README.md).
+
+[`s3fs`](https://github.com/s3fs-fuse/s3fs-fuse) allows Linux and macOS to mount an S3 bucket via FUSE. If you want to learn more about `s3fs-fuse` and FUSE you can do the optional [s3fs lab](../fuse/README.md). 
 
 ![](../images/cos-plugin-architecture.png)
 

workshop/flexvolume/README.md

@@ -0,0 +1,29 @@
+# FlexVolume
+
+The [Kubernetes Storage Special Interest Group (SIG)](https://github.com/kubernetes/community/blob/master/sig-storage) defines three methods to implement a volume plugin:
+
+1. In-tree volume plugin [deprecated],
+2. Out-of-tree FlexVolume driver [deprecated],
+3. Out-of-tree CSI driver.
+
+Flexvolume is deprecated, but the Kubernetes Storage-SIG plans to continue to support and maintain the Flex Volume API. 
+
+As of Kubernetes 1.9, there are two `out-of-tree` methods to implement volume plugins: `Container Storage Interface (CSI)` and `FlexVolume`. 
+
+`Out-of-tree` volume plugins enable storage developers to create custom storage plugins. Before the introduction of the CSI and FlexVolume, all volume plugins were `in-tree` meaning they were built, linked, compiled, and shipped with the core Kubernetes binaries and extend the core Kubernetes API. 
+
+FlexVolume has existed since Kubernetes 1.2, and is a GA feature since Kubernetes 1.8. FlexVolume uses an exec-based model to interface with drivers. The FlexVolume driver binaries must be installed in a pre-defined volume plugin path on each node and in some cases the control plane nodes as well. Pods interact with FlexVolume drivers through the flexvolume in-tree volume plugin.
+
+The plugin expects the following call-outs are implemented for the backend drivers. Call-outs are invoked from Kubelet and Controller Manager.
+
+* Init,
+* Attach,
+* Detach,
+* Wait for attach,
+* Volume is attached,
+* Mount device,
+* Unmount device,
+* Mount,
+* Unmount.
+
+For more information about FlexVolume, see [flex](https://github.com/kubernetes/community/blob/master/contributors/devel/sig-storage/flexvolume.md)