/mcp-health activeConnections always reports 0 regardless of connected clients

[OleksiiKuzmin]

Jenkins and plugins versions report

Environment

Plugin version: 0.172.v9db_cb_43cdb_cc
Jenkins: 2.555.2-lts 
Client: Kiro IDE using Streamable HTTP (/mcp-server/mcp)
Also tested with SSE endpoint (/mcp-server/sse) — same result

What Operating System are you using (both controller, and any agents involved in the problem)?

Jenkins master running as ECS task in AWS from the official Jenkins Docker image:
jenkins/jenkins:2.555.2-lts-jdk21

Reproduction steps

Install mcp-server plugin 0.172.v9db_cb_43cdb_cc on Jenkins

Configure an MCP client (Kiro IDE in this case) with ~/.kiro/settings/mcp.json:

{
  "mcpServers": {
    "jenkins-native": {
      "url": "https://your-jenkins-host/mcp-server/sse",
      "headers": {
        "Authorization": "Basic <base64-encoded-user:token>"
      }
    }
  }
}

Verify the connection works — execute any MCP tool call (e.g. whoAmI or getJobs). Confirm a successful response.

While the client is connected, curl the health endpoint:

curl https://your-jenkins-host/mcp-health
Observe "activeConnections": 0 despite the active session.

Repeat with Streamable HTTP transport:

{
  "mcpServers": {
    "jenkins-native": {
      "url": "https://your-jenkins-host/mcp-server/mcp",
      "headers": {
        "Authorization": "Basic <base64-encoded-user:token>"
      }
    }
  }
}

Same result — activeConnections remains 0.

Expected Results

activeConnections should reflect clients currently connected via any transport (SSE or Streamable HTTP).

Actual Results

The /mcp-health endpoint always returns "activeConnections": 0 even when clients are actively connected and making successful MCP tool calls.

{"mcpServerStatus":"ok","activeConnections":0,"shuttingDown":false,"timestamp":"2026-06-04T17:46:55.989448234Z"}

Anything else?

Impact on Monitoring
When using Prometheus with a JSON Exporter to scrape /mcp-health, the activeConnections metric is permanently 0. This makes it impossible to:
Monitor how many MCP clients are connected
Set alerts on connection counts
Track MCP adoption across teams
Detect when clients disconnect unexpectedly
Make correlation between MCP Server API cals and System Load.

Are you interested in contributing a fix?

No response