Topo lookup tablet type

[sbaker617]

Description

This adds an optional --init_tablet_type_lookup startup flag for vttablet to implement functionality described in this issue.

When present, --init_tablet_type_lookup will result in searching the topology for the current tablet being started. If found, will use the previous tablet type instead of the one passed with --init_tablet_type.

Related Issue(s)

Feature Request: Add ability to restore TabletType on restart based on topology.

Checklist

• "Backport to:" labels have been added if this change should be back-ported to release branches
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Deployment Notes

AI Disclosure

[vitess-bot]

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[ejortegau]

A few comments.

[ejortegau]

Do we want to preserve tablet type PRIMARY? Imagine this:

• vttablet is running as Primary.
• vttablet crashes.
• vtorc fails-over.
• vttablet gets restarted by systemd.
• vttablet restores its tablet type to Primary, but there is already a primary set by vtorc.

[sbaker617]

had initially thought the checkPrimaryShip() would handle any conflicts, but seems like it wouldn't revert the tablet back to REPLICA.

added special handling for type detected previously as PRIMARY to be set to REPLICA, allowing checkPrimaryShip() to set back to PRIMARY if appropriate.
f2eb9b8