Combined configuration file for all roles in cluster mode

[sunng87]

What type of enhancement is this?

Configuration

What does the enhancement do?

Currently we are using configuration file for each role of clusters, in order to customize a cluster, we need to create four files. This approach has a few drawbacks:

• It's difficult for user to understand which function toggle to be configured on which file/role
• It's difficult to share configuration with other people
• It's introducing additional complexity when there is a need to configure one function on each file (remote wal, for example, on both datanode and meta). It's also error-prone.

This situation is also inconsistent with our design philosophy to use one binary for all scenario.

Implementation challenges

Some of the configuration items are highly related to particular instance of the cluster, for example, node_id is only meaning for a datanode instance and cannot share between others. We need a solution for this.