Understanding and Resolving "Upstream Timed Out" Errors in NGINX

Introduction

When deploying applications behind a web server like NGINX, you might encounter timeout errors such as "upstream timed out (110: Connection timed out) while reading response header from upstream." This issue typically arises when the upstream application takes too long to respond to a request. In this tutorial, we’ll explore why these timeouts occur and how to effectively resolve them.

Understanding NGINX and Upstream Servers

NGINX serves as a reverse proxy server that forwards client requests to an upstream server (e.g., Puma, Riak) for processing. The response from the upstream server is then sent back to the client by NGINX. Efficiently managing this interaction requires careful configuration of timeouts to prevent premature connection closures.

Common Causes

1. Long Processing Time: The upstream server might be slow in processing requests due to complex operations or high loads.
2. Misconfigured Timeout Settings: Default timeout settings may not align with the expected response time of your application, leading to unnecessary errors.

Configuring NGINX for Better Performance

To resolve "upstream timed out" errors, consider adjusting various timeout settings in your NGINX configuration files. Here’s how:

1. Increase Timeout Settings

Timeout settings define how long NGINX waits for a response from the upstream server before giving up.

• proxy_connect_timeout: Time to establish a connection with the upstream.
• proxy_send_timeout: Duration to wait while transmitting data to the upstream.
• proxy_read_timeout: Wait time for receiving data back from the upstream. This is often the most critical setting to adjust.

Example configuration:

http {
    proxy_connect_timeout 600s;
    proxy_send_timeout 600s;
    proxy_read_timeout 3600s; # Extended read timeout to prevent premature timeouts.
}

2. Optimize Proxy Buffering

Buffer settings control how NGINX handles data being sent to and from the upstream server, which can affect performance during high loads.

location / {
    proxy_buffer_size 64k;
    proxy_buffers 16 32k; 
    proxy_busy_buffers_size 64k;
    proxy_temp_file_write_size 64k;
}

3. Connection Keep-Alive

Ensure that NGINX manages connections efficiently by tweaking keep-alive settings.

server {
    location / {
        proxy_http_version 1.1;
        proxy_set_header Connection "";
    }
}

This helps in reusing TCP connections for multiple requests, improving performance and reducing the chance of timeouts.

4. Analyze Logs

Logs provide insights into which upstream is causing delays.

• Error Logs: Review logs to identify specific upstream servers timing out.

Example log entry:

upstream timed out (110: Connection timed out) while reading response header from upstream, client: xxxxx, upstream: fastcgi://unix:/var/run/php/php5.6-fpm.sock

Adjust the relevant read timeout for that specific upstream server.

5. Collaborate with Upstream Stakeholders

For long-term solutions, work with developers managing the upstream applications to optimize response times or refactor inefficient operations.

Conclusion

Resolving "upstream timed out" errors in NGINX requires a combination of proper configuration adjustments and collaborative efforts to improve application performance. By understanding how different settings interact and analyzing logs effectively, you can ensure smooth operation and minimize client-facing timeouts.

Remember, while increasing timeout values is sometimes necessary, it’s crucial to also focus on optimizing upstream processes for sustainable improvements.