---
id: 3a23c0c0-edf1-4cd4-b2a3-30550e06d99c
---

# Tomcat High Number of Active Sessions.
---

This incident occurs when the Tomcat server is experiencing an unusually high number of active sessions. Active sessions refer to the number of users currently accessing a web application hosted on the Tomcat server. When the number of active sessions exceeds the server's capacity, it can lead to slow response times, unresponsive applications, or even server crashes. This incident requires immediate attention to resolve the issue and prevent any further impact on the web application's performance.

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

export TOMCAT_PORT="PLACEHOLDER"

export PATH_TO_TOMCAT_SERVER_LOG_FILE="PLACEHOLDER"

export PATH_TO_TOMCAT_CONFIG_FILE="PLACEHOLDER"

export MAX_SESSIONS="PLACEHOLDER"
```

## Debug

### Check the number of active sessions on the Tomcat server
```shell
sudo ${CATALINA_HOME}/bin/catalina.sh sessioncount
```

### Check the current CPU and memory usage of the Tomcat server
```shell
top -p $(pgrep java)
```

### Check the current network connections to the Tomcat server
```shell
sudo netstat -anp | grep ${TOMCAT_PORT}
```

### Check the server log for any errors or warnings related to high session count
```shell
sudo tail -f ${CATALINA_HOME}/logs/catalina.out | grep -i "session"
```

### Check the server log for any errors or warnings related to memory usage
```shell
sudo tail -f ${CATALINA_HOME}/logs/catalina.out | grep -i "memory"
```

### Check the server log for any errors or warnings related to CPU usage
```shell
sudo tail -f ${CATALINA_HOME}/logs/catalina.out | grep -i "cpu"
```

## Repair

### Check the server logs to identify the source of the high number of active sessions. This can help determine if the issue is caused by a specific application or user activity.
```shell


#!/bin/bash



# Define variables

LOG_FILE=${PATH_TO_TOMCAT_SERVER_LOG_FILE}



# Check for high number of active sessions in the log file

if grep -q "High Number of Active Sessions" "$LOG_FILE"; then

    # Identify the source of the high number of active sessions

    SOURCE=$(grep "High Number of Active Sessions" "$LOG_FILE" | awk '{print $5}')

    echo "The high number of active sessions is caused by $SOURCE."

else

    echo "No high number of active sessions detected in the server logs."

fi


```

### Increase the maximum number of active sessions allowed by the Tomcat server to handle the increased traffic. This can be done by modifying the server's configuration file.
```shell
bash

#!/bin/bash



# Define the path to the Tomcat configuration file

config_file=${PATH_TO_TOMCAT_CONFIG_FILE}



# Define the maximum number of active sessions allowed

max_sessions=${MAX_SESSIONS}



# Update the configuration file with the new value

sed -i "s/<Connector port=\"8080\" protocol=\"HTTP\/1.1\"/<Connector port=\"8080\" protocol=\"HTTP\/1.1\" maxActiveSessions=\"$max_sessions\"/g" "$config_file"



# Restart the Tomcat server to apply the changes

systemctl restart tomcat


```

This incident occurs when the Tomcat server is experiencing an unusually high number of active sessions. Active sessions refer to the number of users currently accessing a web application hosted on the Tomcat server. When the number of active sessions exceeds the server's capacity, it can lead to slow response times, unresponsive applications, or even server crashes. This incident requires immediate attention to resolve the issue and prevent any further impact on the web application's performance.


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 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.


Tomcat Servlet Session Replication Failures.

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 occurs when the PermGen or Metaspace usage of the Tomcat server exceeds 90%. PermGen and Metaspace are memory pools used for storing class definitions and metadata of the Java virtual machine (JVM). When these memory pools reach their maximum capacity, the server may experience performance issues or even crash. This incident requires immediate attention from the software engineer to investigate the root cause and take appropriate actions to resolve the issue.


Tomcat PermGen or Metaspace Usage exceeds 90%

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

```shell
export CATALINA_HOME="PLACEHOLDER"

export TOMCAT_PORT="PLACEHOLDER"

export PATH_TO_TOMCAT_SERVER_LOG_FILE="PLACEHOLDER"

export PATH_TO_TOMCAT_CONFIG_FILE="PLACEHOLDER"

export MAX_SESSIONS="PLACEHOLDER"
```


### Check the number of active sessions on the Tomcat server

```shell
sudo ${CATALINA_HOME}/bin/catalina.sh sessioncount
```

### Check the current CPU and memory usage of the Tomcat server

```shell
top -p $(pgrep java)
```

### Check the current network connections to the Tomcat server

```shell
sudo netstat -anp | grep ${TOMCAT_PORT}
```

### Check the server log for any errors or warnings related to high session count

```shell
sudo tail -f ${CATALINA_HOME}/logs/catalina.out | grep -i "session"
```

### Check the server log for any errors or warnings related to memory usage

```shell
sudo tail -f ${CATALINA_HOME}/logs/catalina.out | grep -i "memory"
```

### Check the server log for any errors or warnings related to CPU usage

```shell
sudo tail -f ${CATALINA_HOME}/logs/catalina.out | grep -i "cpu"
```


### Check the server logs to identify the source of the high number of active sessions. This can help determine if the issue is caused by a specific application or user activity.

```shell


#!/bin/bash



# Define variables

LOG_FILE=${PATH_TO_TOMCAT_SERVER_LOG_FILE}



# Check for high number of active sessions in the log file

if grep -q "High Number of Active Sessions" "$LOG_FILE"; then

    # Identify the source of the high number of active sessions

    SOURCE=$(grep "High Number of Active Sessions" "$LOG_FILE" | awk '{print $5}')

    echo "The high number of active sessions is caused by $SOURCE."

else

    echo "No high number of active sessions detected in the server logs."

fi


```

### Increase the maximum number of active sessions allowed by the Tomcat server to handle the increased traffic. This can be done by modifying the server's configuration file.

```shell
bash

#!/bin/bash



# Define the path to the Tomcat configuration file

config_file=${PATH_TO_TOMCAT_CONFIG_FILE}



# Define the maximum number of active sessions allowed

max_sessions=${MAX_SESSIONS}



# Update the configuration file with the new value

sed -i "s/<Connector port=\"8080\" protocol=\"HTTP\/1.1\"/<Connector port=\"8080\" protocol=\"HTTP\/1.1\" maxActiveSessions=\"$max_sessions\"/g" "$config_file"



# Restart the Tomcat server to apply the changes

systemctl restart tomcat


```


Tomcat High Number of Active Sessions.

Overview

Parameters

Debug

Check the number of active sessions on the Tomcat server

Check the current CPU and memory usage of the Tomcat server

Check the current network connections to the Tomcat server

Repair

Check the server logs to identify the source of the high number of active sessions. This can help determine if the issue is caused by a specific application or user activity.

Increase the maximum number of active sessions allowed by the Tomcat server to handle the increased traffic. This can be done by modifying the server's configuration file.

Learn more

Related Runbooks

Tomcat thread pool exhaustion.

Tomcat Servlet Session Replication Failures.

Tomcat Server Crash

Tomcat PermGen or Metaspace Usage exceeds 90%

Support