Feature Description

👋 I would like to be able to start a tablet as DRAINED tablet-type, in order to perform some offline actions. My goal with starting as DRAINED is to:

1. Prevent vtgate from sending traffic to the tablet that is being worked on
2. Prevent VTOrc to fix replication while the tablet is worked on

Today you can start vttablet as only:

• SPARE
• REPLICA
• RDONLY

Unfortunately all of these tablet-types are considered by VTOrc/topo-helpers (validly, in my opinion) as types that must replicate at all times. This means there is no way to start a vttablet that is ignored by VTGate and VTOrc initially. What this can mean in practice is VTOrc intervening or complaining about problems that cannot be fixed, for example ReplicationStopped on a tablet where offline work is occurring

// DRAINED is the type a server goes into when used by Vitess tools
// to perform an offline action. It is a serving type (as
// the tools processes may need to run queries), but it's not used
// to route queries from Vitess users. In this state,
// this tablet is dedicated to the process that uses it.
TabletType_DRAINED TabletType = 8

DRAINED feels like the perfect tablet-type for this case, but it's not in the allow-list of types vttablet can startup as

This issue proposes DRAINED is added to the allow-list so a user can start a tablet that is ignored by VTGate + VTOrc simultaneously

Use Case(s)

A user that wants to bring up a tablet and perform offline work and would like to avoid:

1. VTGate sending traffic to this tablet
2. VTOrc fixing/complaining about problems (eg replication stopped) while offline work occurs

A direct example: is a tablet that is quarantined for investigation. A vttablet that functional but hidden from traffic and simultaneously is not actioned by VTOrc is ideal