How many agents can one VICIdial server handle?

VICIdial does not have a hard configuration option that says "maximum agents: 50." The real limit is the physical box underneath — how many cores it has, how much RAM, and how much disk I/O it can sustain before performance degrades. Understanding what drives agent capacity helps you know when to monitor carefully and when to resize.

What each logged-in agent costs the server

Every Agent session open on the system creates a few steady-state costs. The agent screen itself polls the VICIdial server every few seconds to update status, call timers, and the active Campaign view. Each active session also has a row in the live agent table that the dialer daemon reads before deciding who to route the next call to. Add the Keepalive process that checks each agent's connection is still alive, and you have several database queries and a small slice of CPU per agent, multiplied by every agent logged in at once.

At idle — agents logged in but not on calls, paused, or in Wrap-up time — this overhead is manageable on almost any modern server. The load climbs when agents are actively dialing, because then each agent drives several outbound attempts at once.

How dial ratio multiplies the load

In Predictive dialing mode, the auto-dialer places multiple calls per available agent so that when one answers, an agent is ready. The Dial level — sometimes called the dialing ratio — controls how aggressively this happens. A level of 2.0 means two lines are dialing for every available agent; a level of 4.0 means four. Each of those lines in flight is an open Asterisk channel consuming CPU and memory. So 40 agents at dial level 3 is not 40 units of load — it is closer to 120 channels worth.

This is why agent count alone does not tell you much about capacity. Two operations with 40 agents each — one running at dial level 1.5 and one running at dial level 4.0 — produce very different loads on the same hardware.

The signals that tell you you are near the limit

flowchart TD
  A["More agents log in"] --> B["Agent polling load rises"]
  A --> C["Dialer drives more [[concurrent-calls]]"]
  B --> D["System load climbs"]
  C --> D
  D --> E{"Load > core count?"}
  E -->|No| F["Healthy headroom"]
  E -->|Yes| G["Agent screen lag appears"]
  G --> H["Call quality degrades"]
  H --> I["[[ratio-dialing]] drops accuracy"]
  I --> J["Time to resize or reduce agents"]

The first place problems show up is usually the agent screen becoming sluggish. Agents notice their status changes taking longer to reflect, or the call timer lagging behind reality. On the server side, system load in the Server Performance Report will be running high, and the IDLE CPU percentage will be close to zero during busy periods. If the process count is also climbing, a daemon may be spawning extra workers trying to keep up. Database query time is a secondary signal — when the box is overloaded, queries that normally complete in milliseconds start queuing and returning stale data to the agent screen, which then triggers even more retries and compounds the problem.

Rough rule of thumb

A commonly cited starting point for a Single tenant VPS deployment is roughly 20 to 30 agents per CPU core when running at moderate dial ratios. A 4-core box is therefore a reasonable starting point for a 60 to 80 agent operation at moderate intensity, but that ceiling drops quickly if you push the dial level above 3 or run back-to-back campaigns without pause. Treat this as a starting estimate, not a guarantee — the only reliable ceiling number for your specific operation comes from the Maximum System Stats report after running in production.

For the broader sizing picture — how agents and channels interact together — see the server health and capacity guide. For a look specifically at how many concurrent agents your box has hit historically, the most concurrent agents report shows you the daily peaks.

Want a managed box sized for your agent count from day one? See what a VICIfast server costs — provisioned in under 40 seconds with the Server Performance Report active from first boot.