---
id: 7cd661f1-5730-4f03-8390-a77fb22d5c39
---

# Tomcat Servlet Session Replication Failures.
---

Tomcat Servlet Session Replication Failures occur when a Tomcat server fails to replicate session data between instances. This can result in users losing their session data or being redirected to a different instance, causing disruption to the application's functionality.

### Parameters
```shell
export INSTANCE_NUMBER="PLACEHOLDER"

export TOMCAT_REPLICATION_PORT="PLACEHOLDER"

export NEW_SESSION_TIMEOUT_VALUE_IN_MINUTES="PLACEHOLDER"

```

## Debug

### Check if all Tomcat instances are up and running
```shell
systemctl status tomcat${INSTANCE_NUMBER}.service
```

### Check if session replication is enabled in server.xml
```shell
grep -i "Cluster" /etc/tomcat${INSTANCE_NUMBER}/server.xml
```

### Check if the session data is being replicated between instances
```shell
cat /var/log/tomcat${INSTANCE_NUMBER}/localhost.${INSTANCE_NUMBER}.log | grep -i "Replication"
```

### Check if the session data is being stored correctly in the shared directory
```shell
ls -l /var/lib/tomcat${INSTANCE_NUMBER}/work/localhost/SESSIONS.ser
```

### Check if the firewall is blocking the replication traffic
```shell
iptables -L -n | grep -i "ACCEPT" | grep -i "dport ${TOMCAT_REPLICATION_PORT}"
```

### Check if there are any errors or exceptions in the logs related to session replication
```shell
cat /var/log/tomcat${INSTANCE_NUMBER}/catalina.out | grep -i "error\|exception"
```

## Repair

### If the issue persists, try increasing the session timeout value to allow more time for the session data to be replicated.
```shell


#!/bin/bash

# Set variables

TIMEOUT=${NEW_SESSION_TIMEOUT_VALUE_IN_MINUTES}


# Edit context.xml file to increase session timeout

sed -i "s/<Manager/<Manager sessionTimeout=\"${TIMEOUT}\"/g" /etc/tomcat/conf/server.xml


# Restart Tomcat

systemctl restart tomcat


```

Tomcat Servlet Session Replication Failures occur when a Tomcat server fails to replicate session data between instances. This can result in users losing their session data or being redirected to a different instance, causing disruption to the application's functionality.


When too many requests are sent to a Tomcat server, the thread pools that handle these requests can run out of available threads. This means that incoming requests will not be processed, leading to service degradation or even a complete outage. This incident type is critical for web applications that rely on Tomcat as their application server.


Tomcat thread pool exhaustion.

Tomcat Server Crash incident type refers to a situation where the Tomcat Server, an open-source web server and servlet container, becomes unresponsive and stops functioning. This can result in a complete or partial system outage, leading to a disruption in the delivery of web applications and services. The root cause of the crash can be attributed to a variety of factors such as misconfiguration, network or hardware issues, software bugs, or excessive server load. It is critical to address this incident quickly to minimize the impact on users and restore normal system functionality.


Tomcat Server Crash

This incident type usually occurs when there is a failure in the SSL Handshake process between a client and server running on a Tomcat web server. This can happen for various reasons such as incorrect SSL certificate configuration, cipher suite mismatches, or network connectivity issues. When this type of incident is not resolved quickly, it can lead to downtime or service disruptions for users trying to access the affected service.


Tomcat SSL Handshake Failure Incident

This incident type is related to the Tomcat server, which is a popular open-source Java application server. It occurs when the available threads in the connection pool are running low, which means that there are not enough resources to serve incoming requests. This can cause delays or even failures in the application's performance, impacting the end-user experience. It is important to monitor and address this issue promptly to ensure that the application runs smoothly and efficiently.


Tomcat Low Available Threads in Connection Pool

In software engineering, a large number of suspended threads in Tomcat is an incident type that occurs when a high number of threads are created but are blocked from executing. This can happen due to a variety of reasons, such as slow database queries, network latency, or resource contention. When this occurs, the system may become unresponsive or slow, causing a degradation in performance or even a complete system failure. It is important to investigate and resolve this issue as quickly as possible to ensure the system can continue to function properly.


Tomcat Large Number of Suspended Threads Incident.

```shell
export INSTANCE_NUMBER="PLACEHOLDER"

export TOMCAT_REPLICATION_PORT="PLACEHOLDER"

export NEW_SESSION_TIMEOUT_VALUE_IN_MINUTES="PLACEHOLDER"

```


### Check if all Tomcat instances are up and running

```shell
systemctl status tomcat${INSTANCE_NUMBER}.service
```

### Check if session replication is enabled in server.xml

```shell
grep -i "Cluster" /etc/tomcat${INSTANCE_NUMBER}/server.xml
```

### Check if the session data is being replicated between instances

```shell
cat /var/log/tomcat${INSTANCE_NUMBER}/localhost.${INSTANCE_NUMBER}.log | grep -i "Replication"
```

### Check if the session data is being stored correctly in the shared directory

```shell
ls -l /var/lib/tomcat${INSTANCE_NUMBER}/work/localhost/SESSIONS.ser
```

### Check if the firewall is blocking the replication traffic

```shell
iptables -L -n | grep -i "ACCEPT" | grep -i "dport ${TOMCAT_REPLICATION_PORT}"
```

### Check if there are any errors or exceptions in the logs related to session replication

```shell
cat /var/log/tomcat${INSTANCE_NUMBER}/catalina.out | grep -i "error\|exception"
```


### If the issue persists, try increasing the session timeout value to allow more time for the session data to be replicated.

```shell


#!/bin/bash

# Set variables

TIMEOUT=${NEW_SESSION_TIMEOUT_VALUE_IN_MINUTES}


# Edit context.xml file to increase session timeout

sed -i "s/<Manager/<Manager sessionTimeout=\"${TIMEOUT}\"/g" /etc/tomcat/conf/server.xml


# Restart Tomcat

systemctl restart tomcat


```


Tomcat Servlet Session Replication Failures.

Overview

Parameters

Debug

Check if all Tomcat instances are up and running

Check if session replication is enabled in server.xml

Check if the session data is being replicated between instances

Check if the session data is being stored correctly in the shared directory

Check if the firewall is blocking the replication traffic

Repair

If the issue persists, try increasing the session timeout value to allow more time for the session data to be replicated.

Learn more

Related Runbooks

Tomcat thread pool exhaustion.

Tomcat Server Crash

Tomcat SSL Handshake Failure Incident

Tomcat Low Available Threads in Connection Pool

Support