MID Servers — architecture, sizing, security

Definitive questions

• +What is a MID Server?
• +How do MID Servers authenticate to the instance?
• +What is MID Server clustering?
• +Where should credentials be stored?

Scenario drills

1. Sizing MID Servers for a global rollout

   “5 datacenters, 30k CIs, 2 AWS VPCs. How many MID Servers and where?”

   Approach

   • One cluster per network zone (each DC + each VPC) — never span firewalls.
   • Rule of thumb: 1 MID per ~5k CIs per Discovery cycle. Add a second for HA per zone.
   • Sync credentials via one external vault; MIDs authenticate to the vault, not to a local keystore.

   // mid_server capability rows
   mid.capabilities = ['Discovery','ServiceMapping'];
   mid.ip_ranges    = ['10.42.0.0/16'];

   Alternate approach

   Alternate: use a small 'utility' MID cluster dedicated to integrations (REST/JDBC) separate from Discovery MIDs so long-running jobs don't starve probes.

   Pitfall

   Sharing one MID cluster across firewall zones — probes silently drop and CI counts look correct in dev.