Understanding the concurrent connection limit - what it is and how it affects your application

A connection (or "connect") is the number of concurrent connections from your software to our server.
A thread in your software is a group of connections within a single instance of your software.

Concurrent Connections: What Are They?

Concurrent connections refer to the number of individual network connections that can be active through a proxy at any given time. It's not about the number of threads in your application but the total number of active network connections. If your proxy server allows 100 concurrent connections, it means that no more than 100 connections can be active at once.

Threads and Their Impact on Connections

A thread in software development is a unit of code execution. Many applications operate in a multi-threaded environment, where multiple tasks can run concurrently. However, it's crucial to understand that one thread can open multiple connections at the same time. For example, when emulating a browser with a Chromium engine, a single thread can initiate dozens of connections to load all the elements of a webpage. This can quickly lead to reaching the limit of concurrent connections.

The Issue of Stuck (Unclosed) Connections

Sometimes tools like curl or Java scripts don't close connections after finishing their tasks. These connections remain active for a while, even if they're no longer used. This is due to incorrect script logic, where it waits for a "time out," but the connections are still open from older tasks (60-120 seconds), and then you start a new task, causing the number of concurrent connections to grow rapidly. This can lead to exceeding the allowable limit of active connections on the proxy, even though far fewer are actually in use.

How to Avoid Problems with Connection Limits?

To avoid problems with concurrent connection limits, we recommend:

1. Close Connections: When using tools like curl, ensure that connections are properly closed after the task is done. Use the `--no-keepalive` option or other methods to force connections to close.

2. Manage Threads: Understand that a single thread can open multiple connections. Plan the number of threads based on the limit of concurrent connections.

3. Monitor Connections: Use monitoring tools to track the number of active and stuck connections. This helps identify when and why the limit is exceeded.

4. Adjust Proxy Configuration: If the number of concurrent connections is too low for your load, consider increasing the limit through technical support. Also, check proxy server settings that define timeout or auto-termination of stuck connections.

Purchasing Additional Limits

You can increase the number of concurrent connections for each service. The cost of one additional connection is $0.04 per month, with a minimum of 1,000 connections.

For example:
A service with 500 IPs has 600 concurrent connections (costing $69/month).
You can buy an additional 1,000 concurrent connections for $40/month.
In total, this service would then have 1,600 concurrent connections.

To increase your limit, contact technical support through the ticket system.