PortOffset 0 on multiple servers

[neunhoef]

A customer wanted to use the starter on Windows (irrelevant here) to setup an ArangoDB cluster on multiple machines. They would prefer it if one could make it so that the same ports are used for starter, agent, coordinator (in particular) and dbserver on all machines. Maybe we can detect this automatically, and if this does not work reliably, there should at least be an option in the starter to override the automatic increment of the portOffset and force it to be zero.

[neunhoef]

Related question: If we allow this, can we migrate a previously started cluster with port offset to one offset zero without a complete reinstall.

[ewoutp]

Currently a portOffset is allocated based on the next free offset.
We can change this to the next free portOffset+slaveAddress pair.

However since we can pre-allocate port offsets, and currently a portOffset is only linked to a slave ID, we must forbid that you change the address of a slave after you've pre-allocated a port offset.

Not sure if that leads to new problems.

[ewoutp]

The second issue (migrating clusters from one portOffset scheme to another) would require:

• Different arangodb-starter config files
• Different arangod server config files
• Different arangod server system tables (guessing)

To me this sounds like adding a LOT of complexity for a very small edge case.

[neunhoef]

I see, migration is too complex, so we do not support it. I would be in favour of allocating the next free portOffset+slaveAddress pair.