# Step 4 - Wrap up

We discussed different algorithms of rate limiting and their pros/cons. Algorithms discussed include: 

* Token bucket 
* Leaking bucket 
* Fixed window 
* Sliding window log 
* Sliding window counter 

Then, we discussed the system architecture, rate limiter in a distributed environment, performance optimization and monitoring. Similar to any system design interview questions, there are additional talking points you can mention if time allows: 

* Hard vs soft rate limiting. 
  * Hard: The number of requests cannot exceed the threshold. 
  * Soft: Requests can exceed the threshold for a short period.
* Rate limiting at different levels. In this chapter, we only talked about rate limiting at the application level (HTTP: layer 7). It is possible to apply rate limiting at other layers. For example, you can apply rate limiting by IP addresses using iptables \[15] (IP: layer 3). Note: The Open Systems Interconnection model (OSI model) has 7 layers \[16]: Layer 1: Physical layer, Layer 2: Data link layer, Layer 3: Network layer, Layer 4: Transport layer, Layer 5: Session layer, Layer 6: Presentation layer, Layer 7: Application layer. 
* Avoid being rate-limited. Design your client with best practices: 
  * Use client cache to avoid making frequent API calls. 
  * Understand the limit and do not send too many requests in a short time frame. 
  * Include code to catch exceptions or errors so your client can gracefully recover from exceptions. 
  * Add sufficient back-off time to retry logic.


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