> For the complete documentation index, see [llms.txt](https://platform9.com/kb/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://platform9.com/kb/pcd/storage/volume-services-flapping-due-to-eaddrinuse-in-pf9-comms-service.md).

# Volume Services Flapping Due to EADDRINUSE in pf9-comms Service

## Problem

The volume provisioning failed intermittently as the Storage services on one or more hosts were observed to be repeatedly transitioning between `up` and `down` states, leading to a degraded Persistent Storage Service status.

## Environment

* Private Cloud Director Virtualization - v2025.4 and Higher
* Self-Hosted Private Cloud Director Virtualization - v2025.4 and Higher
* Component: Persistent Storage

## Cause

The issue was caused by communication socket exhaustion on the affected node, leading to port binding failures. Specifically, the `pf9-comms` service was repeatedly logging the following error in `/var/log/pf9/comms/comms.log`:

```bash
EADDRINUSE encountered during SNI client creation ... retrying in 20000 milliseconds
```

This indicates that the required port was already in use or in TIME\_WAIT state, preventing successful socket binding and disrupting communication between services (including volume driver interactions with the backend).

## Diagnostics

1. The following symptoms were observed:
   * The`openstack volume service list` showed cinder-volume in down state intermittently.
   * The `/var/log/pf9/comms/comms.log` contained repeated `EADDRINUSE` errors.
2. The `/var/log/pf9/cindervolume-base` logs on the cinder host showed API communication failures to the Tintri backend, including:

```bash
reached maximum retry attempts: 2, reason: Volume driver reported an error:  (source: CinderDriver, typeId: com.tintri.api.rest.v310.dto.domain.beans.TintriError, code: ERR-API-8001)
```

Network and Tintri API endpoints were reachable, and credentials were valid, ruling out direct storage backend issues.

## Resolution

1. Restarted the pf9-comms service on the affected Cinder volume host:

```bash
$ sudo systemctl restart pf9-comms
```

2. Post-restart, the EADDRINUSE messages no longer appeared in comms.log.
3. The `cinder-volume` services returned to `up` state:

```bash
$ openstack volume service list -c Binary -c Host -c Status -c State

+-----------------+----------------------------------+---------+------+
| Binary          | Host                             | Status  | State|
+-----------------+----------------------------------+---------+------+
| cinder-scheduler| cinder-scheduler-[ID]            | enabled | up   |
| cinder-volume   | [CINDER_HOST_ID]@[CINDER_BACKEND]| enabled | up   |
+-----------------+----------------------------------+---------+------+
```

4. Verified volume provisioning functionality and ensured that backend API communication was stable.

## Validation

* Monitored the `cinder-volume` service status using the `openstack volume service list`for **30 minutes** and confirmed that the services remained in the `up` state.
* No further `EADDRINUSE` errors were observed in `comms.log`.
* Volume creation and attachment operations succeeded.

## Additional Information

* `EADDRINUSE` indicates that a socket binding operation failed due to the port already being in use.
* This is often caused by:
  * A large number of short-lived TCP connections
  * Delays in socket cleanup
  * Insufficient ephemeral port ranges or low timeout settings
* Restarting the communication layer (`pf9-comms`) forces the cleanup of stale sockets and refreshes the SNI client sessions.


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