Is it practical to mount a block storage to multiple VPS running Docker Swarm for shared storage?

Question

Looking at multiple options to implement a shared storage for a Docker Swarm, I can see most of them require a special Docker plugin:

• sshFs
• CephFS
• glusterFS
• S3
• and others

... but one thing that is not mentioned anywhere is just mounting a typical block storage to all VPS nodes running the Docker Swarm. Is this option impractical and thus not mentioned on the Internet? Am I missing something?

My idea is as follows:

1. Create a typical Block Storage (like e.g. one offered by DigitalOcean or Vultr).
2. Mount it to your VPS filesystem.
3. Mount a folder from that Block Storage as a volume in the Docker Container / Docker Worker with using a "local" driver.

Sounds the simplest and most obvious to me. Why people are using more complicated setups like sshFs, CephFS etc? And most importantly, is the implementation I described viable, and if so, what are the drawbacks of doing it this way?

Answer 1

The principal advantage of using a volume plugin over mounted storage comes down to the ability to create storage volumes dynamically, and associate them with namespaces.

i.e. with docker managing storage for a volume via a "volumes: data:" directive in a compose file, a volume will be created for each named stack that is deployed.

Using the local driver and mounts, you the swarm admin now need to ensure that no two stacks are trying to use /mnt/data.

Once you pass that hurdle, some platforms have limitations to the number of hosts a block storage can be mounted on to.

Theres also the security angle to consider - with the volume mapped like that a compromose to any service on any host can potentially expose all your data to an attacker, where a volume plugin will expose just exactly the data mounted on that container.

All that said - docker swarm is awesome and the current plugin space is lacking - if mounting block storage is what it takes to get a workable storage solution I say do it. Hopefully the CSI support will be ready before year end however.