Cheat sheet
System design building blocks
Every major component on one page. Select a term to open its lesson.
Networking
- DNS
- Turns domain names into IP addresses; can route by geography or health.
- Load balancer
- Spreads traffic across healthy servers at layer 4 or layer 7.
- CDN
- Edge caches that serve static content close to users.
- Reverse proxy
- Forwards requests to back ends; handles TLS, compression, caching.
- API gateway
- Single entry point applying auth, limits and routing.
- Firewall / WAF
- Blocks disallowed traffic and common web attacks.
- VPN / private link
- Private, encrypted connectivity between networks.
Compute
- Virtual machines
- Full control of the OS; you patch and scale them.
- Containers
- Package an app with its dependencies; start in seconds.
- Kubernetes
- Orchestrates containers with self-healing and scaling.
- Serverless functions
- Code that runs per event; pay per execution.
- PaaS
- Managed app hosting: you deploy code, the platform runs it.
Storage
- Relational database
- Tables, joins, ACID transactions.
- NoSQL
- Document, key-value, wide-column and graph stores.
- Object storage
- Cheap, durable storage for files and blobs.
- Block / file storage
- Disks attached to VMs; shared network file systems.
- Cache
- In-memory store for hot data, with TTLs.
- Search engine
- Full-text and faceted search over indexed documents.
Communication
- REST / GraphQL / gRPC
- Request-response API styles for different clients.
- WebSocket / SSE
- Push updates to clients in real time.
- Message queue
- Hand work to background consumers.
- Pub/sub & streaming
- Broadcast events to many subscribers; replayable logs.
- Service mesh
- mTLS, retries and telemetry between services.
Security
- Authentication
- Prove identity: OAuth 2.0, OIDC, MFA, passkeys.
- Authorization
- Decide access: roles (RBAC), attributes (ABAC), ownership checks.
- SSO
- One sign-in through a central identity provider.
- Encryption
- TLS in transit; encryption at rest with managed keys.
- Secrets management
- Keys and passwords in a vault, rotated automatically.
- Rate limiting
- Stops abuse and enforces fair use.
Observability
- Logs
- Structured records of events.
- Metrics
- Rates, errors, latency percentiles, saturation.
- Traces
- One request followed across services.
- Alerts & SLOs
- Notify on user impact against agreed objectives.
Architecture
- Monolith / modular monolith
- One deployable, ideally with strong module boundaries.
- Microservices
- Independently deployable services owning their data.
- Event-driven
- Components react to events through a broker.
- CQRS
- Separate models for writes and reads.
- Saga
- Cross-service transactions with compensations.
Scalability & reliability
- Vertical / horizontal scaling
- Bigger machine, or more machines.
- Replication
- Copies of data for reads and failover.
- Sharding
- Split data across databases by a key.
- Redundancy
- No single point of failure; spread across zones.
- Circuit breaker & retries
- Contain failures and recover from transient errors.
- Idempotency
- Make retries safe for operations with side effects.
- Backups & disaster recovery
- Tested restores, defined RPO and RTO.