Expose some configuration values via SHOW DIAGNOSTICS

[mark-rushakoff]

To reduce back-and-forth cycles between developers and users, we should include a subset of runtime configuration values in the output of SHOW DIAGNOSTICS. We already ask for diagnostics output in our issue template.

Rationale

• SHOW DIAGNOSTICS output will reflect any configuration set as environment variables (which is higher precedence than the config file)
• Diagnostics output is available without needing shell access to the machine running InfluxDB and without knowing where the config file resides on disk
• Diagnostics output will not contain large and numerous blocks of comments like most config files do, so it will be easier for developers to read

Example configuration settings likely to be included

A configuration setting is likely to be included if it will help us diagnose issues users are experiencing.

• data.cache-snapshot-memory-size
• http.https-enabled
• udp.batch-timeout

Example configuration settings likely to be excluded

A configuration setting will not be included if it is not helpful in troubleshooting or if exposing that value would make the system less secure.

• data.query-log-enabled: whether certain logs are enabled is usually not interesting to developers
• http.shared-secret: security-related, should not be exposed via any external tooling