---
id: 50eb908c-5880-4f40-899e-9989ed450517
---

# Mod_jk Load Balancing Issues in Apache HTTP.
---

This incident type refers to a problem with the load balancing functionality of the Apache HTTP server when using the mod_jk connector. This can cause issues with distributing incoming traffic across multiple servers, resulting in reduced performance or even downtime for the affected services. It is important to address and resolve these issues as quickly as possible to minimize impact on users and ensure the stability of the system.

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

export PORT="PLACEHOLDER"

export WORKER_NODE_1="PLACEHOLDER"

export WORKER_NODE_2="PLACEHOLDER"

export LOADBALANCER="PLACEHOLDER"

export DESIRED_LOAD_BALANCING_ALGORITHM="PLACEHOLDER"

export PATH_TO_MOD_JK_CONFIGURATION_FILE="PLACEHOLDER"
```

## Debug

### Check if mod_jk is enabled in Apache HTTP
```shell
apachectl -M | grep ${MOD_JK}
```

### Check if the load balancer is configured correctly
```shell
grep -r '<LoadBalancer' /etc/httpd/conf.d/
```

### Check the status of the worker nodes
```shell
curl http://${WORKER_NODE_1}:${PORT}/status

curl http://${WORKER_NODE_2}:${PORT}/status
```

### Check the Apache error log for any relevant error messages
```shell
tail -n 100 /var/log/httpd/error_log | grep ${MOD_JK}
```

### Check the Apache access log for any relevant traffic patterns
```shell
tail -n 100 /var/log/httpd/access_log | grep ${LOADBALANCER}
```

### Check the network connectivity between the load balancer and worker nodes
```shell
ping -c 5 ${WORKER_NODE_1}

ping -c 5 ${WORKER_NODE_2}
```

## Repair

### Restart Apache HTTP server to see if the issue is resolved temporarily.
```shell


#!/bin/bash



# Stop the Apache HTTP server

sudo systemctl stop apache2



# Wait for a few seconds to ensure that all services are stopped

sleep 5



# Start the Apache HTTP server

sudo systemctl start apache2



# Check the status of the Apache HTTP server

sudo systemctl status apache2


```

### Adjust the load balancing algorithm used by mod_jk to better suit the specific needs of the system and its traffic patterns.
```shell


#!/bin/bash



# Define variables

LOAD_BALANCER_CONF=${PATH_TO_MOD_JK_CONFIGURATION_FILE}

NEW_ALGORITHM=${DESIRED_LOAD_BALANCING_ALGORITHM}



# Stop Apache HTTP server

systemctl stop httpd



# Update mod_jk configuration file with new load balancing algorithm

sed -i "s/^worker.loadbalancer.type=.*$/worker.loadbalancer.type=$NEW_ALGORITHM/" $LOAD_BALANCER_CONF



# Start Apache HTTP server

systemctl start httpd


```

This incident type refers to a problem with the load balancing functionality of the Apache HTTP server when using the mod\_jk connector. This can cause issues with distributing incoming traffic across multiple servers, resulting in reduced performance or even downtime for the affected services. It is important to address and resolve these issues as quickly as possible to minimize impact on users and ensure the stability of the system.


This incident type refers to frequent mismatches between the virtual hosts configured on an Apache server. This can cause issues with routing traffic to the intended web application or website, resulting in downtime or other problems. It is important to address these mismatches promptly to ensure the proper functioning of the server and any associated applications.


Virtual Host Mismatches on Apache Server.

The Slowloris Attack is a type of Denial of Service (DoS) attack that exploits a vulnerability in the Apache web server. It works by sending HTTP requests to the server and keeping those connections open for as long as possible, thereby using up all the available resources of the server and rendering it unresponsive to legitimate requests. As a result, the server becomes slow or unresponsive, causing downtime for the affected website or service. This type of attack can be detected and mitigated by implementing specific security measures and tools.


Slowloris Attack Detected on Apache server.

This incident type refers to a security vulnerability in the SSL/TLS configuration of the Apache HTTP Server, which can leave the server and its users vulnerable to attacks. The SSL/TLS configuration is responsible for encrypting the communication between the server and its clients, and if it is not configured properly, it can be exploited by hackers to intercept or modify sensitive data. This type of incident requires immediate attention from software engineers to ensure that the SSL/TLS configuration is properly configured to prevent any potential security threats.


Inadequate SSL/TLS Configuration for Apache HTTP Server.

This incident type refers to a situation where the number of child processes created by an Apache server reaches a high threshold, causing performance issues and potentially leading to server crashes. This can occur due to factors such as high traffic volume or misconfigured server settings. The incident requires investigation and mitigation to restore normal server functioning and prevent future occurrences.


High Number of Apache Child Processes Incident

This incident type refers to a situation where the Apache server running on a system is consuming an abnormally high amount of memory. This can result in the system becoming unresponsive or slow, leading to degraded performance. It is important to identify the root cause of the high memory usage and take appropriate measures to optimize the server's performance to avoid such incidents in the future.


High Memory Usage by Apache

```shell
export MOD_JK="PLACEHOLDER"

export PORT="PLACEHOLDER"

export WORKER_NODE_1="PLACEHOLDER"

export WORKER_NODE_2="PLACEHOLDER"

export LOADBALANCER="PLACEHOLDER"

export DESIRED_LOAD_BALANCING_ALGORITHM="PLACEHOLDER"

export PATH_TO_MOD_JK_CONFIGURATION_FILE="PLACEHOLDER"
```


### Check if mod\_jk is enabled in Apache HTTP

```shell
apachectl -M | grep ${MOD_JK}
```

### Check if the load balancer is configured correctly

```shell
grep -r '<LoadBalancer' /etc/httpd/conf.d/
```

### Check the status of the worker nodes

```shell
curl http://${WORKER_NODE_1}:${PORT}/status

curl http://${WORKER_NODE_2}:${PORT}/status
```

### Check the Apache error log for any relevant error messages

```shell
tail -n 100 /var/log/httpd/error_log | grep ${MOD_JK}
```

### Check the Apache access log for any relevant traffic patterns

```shell
tail -n 100 /var/log/httpd/access_log | grep ${LOADBALANCER}
```

### Check the network connectivity between the load balancer and worker nodes

```shell
ping -c 5 ${WORKER_NODE_1}

ping -c 5 ${WORKER_NODE_2}
```


### Restart Apache HTTP server to see if the issue is resolved temporarily.

```shell


#!/bin/bash



# Stop the Apache HTTP server

sudo systemctl stop apache2



# Wait for a few seconds to ensure that all services are stopped

sleep 5



# Start the Apache HTTP server

sudo systemctl start apache2



# Check the status of the Apache HTTP server

sudo systemctl status apache2


```

### Adjust the load balancing algorithm used by mod\_jk to better suit the specific needs of the system and its traffic patterns.

```shell


#!/bin/bash



# Define variables

LOAD_BALANCER_CONF=${PATH_TO_MOD_JK_CONFIGURATION_FILE}

NEW_ALGORITHM=${DESIRED_LOAD_BALANCING_ALGORITHM}



# Stop Apache HTTP server

systemctl stop httpd



# Update mod_jk configuration file with new load balancing algorithm

sed -i "s/^worker.loadbalancer.type=.*$/worker.loadbalancer.type=$NEW_ALGORITHM/" $LOAD_BALANCER_CONF



# Start Apache HTTP server

systemctl start httpd


```


Mod_jk Load Balancing Issues in Apache HTTP.

Overview

Parameters

Debug

Check if mod_jk is enabled in Apache HTTP

Check if the load balancer is configured correctly

Check the status of the worker nodes

Check the Apache error log for any relevant error messages

Check the Apache access log for any relevant traffic patterns

Check the network connectivity between the load balancer and worker nodes

Repair

Restart Apache HTTP server to see if the issue is resolved temporarily.

Adjust the load balancing algorithm used by mod_jk to better suit the specific needs of the system and its traffic patterns.

Learn more

Related Runbooks

Virtual Host Mismatches on Apache Server.

Slowloris Attack Detected on Apache server.

Inadequate SSL/TLS Configuration for Apache HTTP Server.

High Number of Apache Child Processes Incident

Support