Analysis and solution for Redis connection rejection problem

Preface

In distributed systems, Redis is a high-performance in-memory database and is widely used in caching, message queueing, session management and other scenarios. However, as the system complexity and concurrency increase, Redis connection problems occur from time to time, especially "reject connection" errors. This article will take the actual log as an example to deeply analyze the common reasons why Redis refuses to connect, and explain in detail the solutions to each reason, helping developers quickly locate problems and ensure the stable operation of Redis services.

1. Problem description

During the project running, we encountered a Redis rejection error, and the error log is as follows:

: Could not get a resource from the pool
    at (:53)
    at (:226)
...
Caused by: : Reject connection (Connection refused)
    at (Native Method)
    at (:350)
    ...

As can be seen from the log, the problem occurs when the connection request between the Jedis client and the Redis server is denied. This error is usually caused by problems such as network configuration, service status, and permission settings. Next, we will analyze the possible causes one by one and provide corresponding solutions.

2. Analysis of common reasons why Redis refuses to connect

2.1 Redis service not started

The most common situation is that the Redis service fails to start normally. When the client tries to connect to Redis, if the service is not running, the connection request is denied. To confirm this, you can check the running status of Redis through the following command:

systemctl status redis

If the Redis service is not started, the command output will display a state similar to "inactive" or "dead". At this point, starting the Redis service can solve the problem:

systemctl start redis

After startup, you can check the status of Redis again to ensure it is running normally.

2.2 Problems with binding address in Redis configuration

By default, Redis may only listen to local loopback addresses127.0.0.1. When a client tries to connect to Redis from an external address, the connection is denied. This usually happens when Redis is deployed on the server, but the client tries to connect from remotely.

To solve this problem, you need to modify the Redis configuration file. First, find the following configuration items:

bind 127.0.0.1

Modify it to:

bind 0.0.0.0

After modification,0.0.0.0Indicates that Redis will listen to all network interfaces and allow external clients to connect. In order for the configuration to take effect, the Redis service needs to be restarted:

systemctl restart redis

In this way, the client can connect to the Redis server from different network interfaces.

2.3 Firewall or security group issues

Sometimes, the server's firewall configuration or the cloud provider's security group limits access to the Redis port. The default port of Redis is6379, If this port is disabled in a firewall or security group, external clients cannot connect.

First, check the server's firewall settings:

iptables -L

If the port is found6379If blocked, it can be allowed to pass through:

iptables -A INPUT -p tcp --dport 6379 -j ACCEPT

Similarly, in a cloud server environment, you need to log in to the cloud platform management console to find the security group configuration of the instance, and ensure that the inbound rules allow it.6379Traffic on the port.

2.4 Redis connection pool exhausted

As can be seen from "Could not get a resource from the pool" in the error log, the Redis connection pool may have been exhausted and cannot allocate resources for the new connection. This is usually caused by a connection leak or excessive concurrency.

The configuration of the Redis connection pool can affect its performance. Developers can adjust the configuration of the connection pool to adapt to the actual load requirements of the system. For example, increase the maximum number of connections in the connection pool maxTotal and ensure that the idle connection can be released in time. In addition, developers should also check whether the connection is not closed in the code to ensure that the connection can be released correctly after use and avoid connection leakage.

Find the program's configuration file and set the corresponding settings, such as tomcat8/webapps/ROOT/WEB-INF/classes/, modify the value. For example, if it was originally 100 and changed to 200, the problem can be temporarily solved.

2.5 Redis server load is too high

When the Redis server is carrying too high load, system resources (such as CPU, memory, network bandwidth) may not be able to support a large number of concurrent connections, resulting in rejection of new connection requests. You can view the status of the Redis server through the following command:

redis-cli info

This command will return detailed information about the current status of Redis, including memory usage, number of connections, command execution, etc. If you find that the resource is used too much, you can consider the following optimization strategies:

• Increase server hardware resources, such as upgrading CPU and memory.
• Use Redis cluster or master-slave architecture to distribute the load across multiple nodes.
• Optimize the cache strategy used by Redis to reduce memory usage.

2.6 Permission configuration issues

If Redis has an authentication mechanism configured (requirepass), but the client does not provide the password correctly, the connection is denied. In this case, the developer needs to make sure that the correct password is used when connecting:

In the Redis configuration file, check if there are configuration items similar to the following:

requirepass yourpassword

When connecting to the client, you need to provide correct authentication information through Jedis:

("yourpassword");

If password verification is not configured, this item can be commented out or removed to allow the client to connect without password.

3. In-depth solutions and optimization suggestions

When encountering the problem of Redis refusing to connect, the key to solving the problem is to quickly locate the cause and prescribe the right medicine. To do this, it is recommended that developers follow the following steps when dealing with Redis connection issues:

1. Check Redis service status: Ensure that the service starts normally and listen for the correct network interface.
2. Network configuration: Verify that the network configurations such as firewall, security group, Redis binding address, etc. are correct.
3. Optimize connection pool configuration: Adjust the connection pool size according to actual load requirements to avoid resource exhaustion.
4. Monitor Redis performance:useredis-cli infoThe command periodically checks the performance status of Redis to ensure that the system resources are sufficient to handle requests.
5. Enhance system flexibility: In high concurrency scenarios, consider adopting Redis cluster or master-slave architecture to improve the scalability and fault tolerance of the system.

4. Summary

As an efficient in-memory database, Redis is widely used in various Internet applications. However, connection problems like "reject connection" inevitably occur in complex systems. Through gradual investigation of possible causes and targeted optimization of configuration, developers can effectively avoid such problems and ensure the stability and performance of the system.

Through a detailed analysis of Redis connection rejection problem, this article covers multiple levels from service status, network configuration to connection pool optimization and performance monitoring. It is hoped that through these steps and solutions, developers can better maintain and optimize Redis services in the production environment and ensure their efficient operation.

Redis connection problems are often the result of increased system complexity and increased concurrency. Through an in-depth understanding of service configuration, network architecture, and resource allocation, developers can prevent and resolve most Redis connection failures. In the future, with the continuous development and optimization of Redis, users also need to continuously improve their ability to optimize performance and troubleshoot problems to ensure the reliability and scalability of the system.

The above is the detailed content of the analysis and solution of Redis rejection connection problem. For more information about Redis rejection connection problem, please follow my other related articles!