Docker Volume Plugin: Google Cloud Storage

Reserving up front a persistent disk of several 10s of GB might not seem like the best idea for some simple container use cases, let's look at an on-demand elastic bucket storage platform: Google Cloud Storage.

Overview

The goal is to use a storage bucket as a docker volume:

a volume would be accessible to containers running on different hosts (maybe not from same cloud provider, or even on local VM, or "native" containers on Mac)
direct access to the volume from the Google Cloud Storage web platform

Screencast - Youtube video

File System

Any volume needs to expose a file system to handle the "disk" I/O, however a storage bucket does not expose any.
Solution: Google Cloud Platform gcsfuse:
Cloud Storage FUSE is an open source Fuse adapter that allows you to mount Google Cloud Storage buckets as file systems on Linux or OS X systems

Installation

Install Google Cloud Platform gcsfuse

https://github.com/GoogleCloudPlatform/gcsfuse/blob/master/docs/installing.md

Install the Volume Driver

$ go get github.com/craimbert/docker-volume-gc-storage
$ go install github.com/craimbert/docker-volume-gc-storage

Stop Docker engine (Debian)

$ service docker stop

Generate on GCP a Service Account key in JSON format

Section To generate a private key in JSON or PKCS12 format:
https://cloud.google.com/storage/docs/authentication?hl=en#generating-a-private-key

Start the Volume Driver (Debian)

$ docker-volume-gc-storage -gcp-key-json gcp-srv-account-key.json

Start Docker engine

$ service docker start

Usage

Create a volume

$ docker volume create --driver gcstorage --name datastore
datastore

The GCS Bucket name is defined by: gcsProjectID_volumeName

List volumes

$ docker volume ls
DRIVER              VOLUME NAME
gcstorage           datastore

Mount the volume on a container

$ docker run -it --rm -v datastore:/tmp alpine sh
/ # date > /tmp/date

The container dir /tmp is mounted on the GC Storage bucket defined by the volume datastore (through the host mountpoint /var/lib/docker-volumes/gcstorage/datastore/_data), the filesystem IO between host mountpoint and GCS bucket being handled by gcsfuse

Upload manually through Cloud Storage web portal a new foo file into the bucket:

Inside the container, the new file foo appears:

/tmp # ls -l /tmp/
total 1
-rw-r--r--    1 root     root            29 Jul  7 02:17 date
-rw-r--r--    1 root     root             4 Jul  7 03:50 foo

Useful Links

Google GO API

Docker Volume Driver interface

https://github.com/docker/go-plugins-helpers/blob/master/volume

##Tested environment: Go & Docker versions

$ go version
go version go1.6.2 linux/amd64

$ docker version
Client:
 Version:      1.11.2
 API version:  1.23
 Go version:   go1.5.4
 Git commit:   b9f10c9
 Built:        Wed Jun  1 21:23:39 2016
 OS/Arch:      linux/amd64
Server:
 Version:      1.11.2
 API version:  1.23
 Go version:   go1.5.4
 Git commit:   b9f10c9
 Built:        Wed Jun  1 21:23:39 2016
 OS/Arch:      linux/amd64

Common Issues

NTP needs to be running on the host in order to use Google APIs

TODO

On Docker for Mac: Docker engine doesn't seem to register the Volume Driver (even after engine restart):

$ docker volume create --driver gcstorage --name datastore
Error response from daemon: create datastore: create datastore: Error looking up volume plugin gcstorage: plugin not found
```
When actually the plugin seems to be referenced properly and behaves correctly (checking via HTTP Remote API):
```
$ cat /etc/docker/plugins/gcstorage.spec
tcp://127.0.0.1:8080

$ curl \
    -X POST \
    -d '{}' \
    http://127.0.0.1:8080/Plugin.Activate
{"Implements": ["VolumeDriver"]}

$ curl \
    -X POST \
    -d '{}' \
    http://127.0.0.1:8080/VolumeDriver.List

$ curl \
    -X POST \
    -d '{"Name": "datastore", "Opts": {}}' \
    http://127.0.0.1:8080/VolumeDriver.Create

$ curl \
    -X POST \
    -d '{}' \
    http://127.0.0.1:8080/VolumeDriver.List
{"Mountpoint":"","Err":"","Volumes":[{"Name":"datastore","Mountpoint":"/var/lib/docker-volumes/gcstorage/datastore/_data"}],"Volume":null,"Capabilities":{"Scope":""}}

$ curl \
    -X POST \
    -d '{"Name": "datastore"}' \
    http://127.0.0.1:8080/VolumeDriver.Get
{"Mountpoint":"","Err":"","Volumes":null,"Volume":{"Name":"datastore","Mountpoint":"/var/lib/docker-volumes/gcstorage/datastore/_data"},"Capabilities":{"Scope":""}}

$ tree /var/lib/docker-volumes/gcstorage
/var/lib/docker-volumes/gcstorage
└── datastore
    └── _data

ravjot28/docker-volume-gc-storage