Pods should allow running other pods as applications

[mildred]

Pods currently only allow running applications backed up by ACI images. This is nice, but it makes it difficult to pack complex applications in multiple containers.

Instead, if pods allowed to specify applications as a pod instance, it would be possible to pack complex applications in multi levels. First, applications requiring multiple service to run together might run as the innermost pods, and the application themselves could interact as the outermost pod.

Example running multiple level applications could be:

• HTTP service for a given host
  • reverse proxy for the following two applications
  • HTTP application 1
    • HTTP server
    • Database
  • HTTP application 2
    • HTTP server
    • Database
    • Processing agent
• Mail service (grouping the different services that need to be configured together)
  • SMTP service
  • IMAP service

On the host, you'll just configure the execution of two pods: the HTTP pod and the Mail pod. They will recursively execute the Mail services and theHTTP reverse proxy, along with both HTTP applications and their database.

[jonboulle]

This is kind of an interesting idea but very underdefined and raises a tonne of questions. For example, what namespaces are shared between the top-level pods? Can isolators be applied at every level? How many levels of nesting are allowed? What about pod lifecycle? (#276)