Tauseef FayyazA to Z
Glossary
Every concept in this sheet, plus the smaller terms it uses. Select a concept to open its card.
A
- Availability and the nines
- Availability is the share of time a system serves requests successfully, usually written as nines. 99.9% allows about 43 minutes of downtime a month, 99.99% about 4.3 minutes.
C
- Cache eviction policies
- When a cache is full, an eviction policy decides what to remove.
- Cache invalidation and TTL
- Invalidation removes or refreshes cached data when the source changes.
- Cache stampede
- A cache stampede happens when a popular key expires and many requests miss at once, all hitting the database to rebuild the same value.
- Cache-aside
- The application checks the cache first.
- CDN
- A content delivery network is a set of servers around the world that cache content close to users.
L
- Latency vs throughput
- Latency is how long one request takes.
- Load balancer (L4 vs L7)
- A load balancer spreads incoming requests across healthy servers.
- Load balancing algorithms
- Round robin sends requests to servers in turn.
P
- Percentile latency (p50, p95, p99)
- The p99 is the latency that 99% of requests beat.
R
- Redundancy and single points of failure
- A single point of failure is any component whose failure takes the whole system down.
- Reverse proxy and API gateway
- A reverse proxy receives client requests and forwards them to backend servers, handling TLS, compression and caching.
S
- SLI, SLO and SLA
- An SLI is a measured indicator, such as the share of requests under 300 ms.
- Stateless services
- A stateless service keeps no per-user data between requests in its own memory.
V
- Vertical vs horizontal scaling
- Vertical scaling gives one machine more CPU, memory or disk.