Airbnb DevOps Engineer System Design Questions

To enhance the performance of serving frequently accessed API responses on Airbnb's platform, an LRU (Least Recently Used) cache can help store the most relevant data while evicting the least needed data efficiently.
Problem statement: Implement an LRUCache class that provides an API for setting and getting values while maintaining the least recently used order.
- def __init__(self, capacity: int) -> None: Initializes the cache with a given capacity.
- def get(self, key: int) -> int: Retrieves the value associated with key, returning -1 if it does not exist.
- def put(self, key: int, value: int) -> None: Updates or inserts the value for key and makes it the most recently used item.
Example 1:
Input: capacity = 2, commands = [(put, 1, 1), (put, 2, 2), (get, 1), (put, 3, 3), (get, 2), (put, 4, 4), (get, 1), (get, 3), (get, 4)]
Output: [None, None, 1, None, -1, None, -1, 3, 4]
Explanation: Accessing keys makes them recent. Therefore, the evicted key was 2 after adding 3.
Constraints:
- The cache capacity will be between 1 and 1000.
- The all keys will be positive integers.

Monitoring service health is essential for Airbnb to ensure that we maintain a reliable platform for our users. An effective health monitor can proactively identify issues before they impact user experience.
Problem statement: Design a class HealthMonitor that maintains a binary tree structure of services, allowing traversal and health-checking of each service node based on different conditions.
- def __init__(self, service_id: str) -> None: Initializes a service with the given ID.
- def add_service(self, service_id: str, parent_id: str) -> None: Adds a child service under a specified parent service.
- def check_health(self) -> List[str]: Returns a list of service IDs that are unhealthy based on some predefined health criteria.
Example 1:
Input: Service Structure: A -> B -> C (A as root)
Output: ['B', 'C']
Explanation: Assuming B and C report unhealthy status during the health check process.
Constraints:
- Each node can have multiple children, but no more than 10.
- All service IDs are unique strings.