What Angel is referring to is that Alfresco CE does not support clustering. So if you want to run multiple Alfresco CE Repository DOcker containers in parallel, each needs to have its own runtime data, i.e. have a separate database and content store, so the data does not get intertwined / mixed up. Alfresco Share never needs a database itself, but if you have two Repository containers with distinct databases / content stores running, you will also need to run two Share containers - one for each Repository.
I think a basic question you should probably provide an answer to is what do you want to achieve with running multiple Alfresco CE Repository containers in parallel? Does it have to do with scalability, failover or load balancing, or do you just want to have two (separate) systems on the same host? What Angel and I answered addresses more the second option. The first option is - as I said - not supported with Alfresco CE in the out-of-the-box state. There is an addon though that has just been open sourced which may help with some of the scalability aspects.
