Support different volume sources for container workload

[hongchaodeng]

An app usually needs some volume of storage, and the storage could be on host (hostPath) or remote (NAS, EBS).

This is usually provided in the app configuration. I would propose to add a Volume abstraction just like what k8s provides and have container volumeMounts section.

[technosophos]

I think when we discussed this months ago, the feeling was that infrastructure operators are typically the ones who decide which storage backs which things. Again, I'm not sure how infrastructure-neutral this is, but will ask around to see.

[vturecek]

Yeah I remember discussing this and the general idea was:

The application developer needs to specify the mount path, which the developer's code depends on. Thus, the component schematic has a volume mount path setting.

The infrastructure operator needs to set up some backing storage for volumes, whether it's a network file system or a cloud storage solution. This is infrastructure-specific, and thus it is not done in the Hydra spec.

The application operator decides where volume data is stored based on the available storage solutions provided by the infrastructure operator. Since the storage solution may have platform-specific connection settings (URL, credentials, partition keys, etc.), the application operator would use a volume mapper trait that is specific to a runtime to connect the storage solution to the volume mount in a component.

[resouer]

"volume mapper trait " looks good to me.

Though developers may have app side requirements like "my awesome app require high performance storage" which could be defined as parameters of app. WDYT? @hongchaodeng

[mikkelhegn]

    resources:
      storage:
        iops-required: 1.000
        read-required: 40 MB/sec
        write-required: 10 MB/sec

Don't put too much in to the numbers, but I think it's the right abstraction in the model.

[hongchaodeng]

Not sure if this feels intuitive, but in our case developers choose the volume size and storage type.

Specifying iops or performance requirements might sound favorable in building a modern platform, but we are not there yet. Our developers choose local or remote disk and setting the size.