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Lessons (40)

• 10,000 Users Do Not Need 10,000 Database Connections

  … context A Node.js service has ten instances, each with a 20-connection pool. Traffic grows and autoscaling …

• Kafka vs RabbitMQ & the Kafka Ecosystem

  … Connect DW[(Data warehouse<br/ Snowflake / BigQuery)] K -- Connect ES[(Elasticsearch)] K -- consumers Svc[Services] Kafka Connect: integration …

• Networking, DNS and Traffic Routing

  … Trace DNS resolution, connection establishment, TLS termination, reverse proxy and backend selection as separate steps. 2. Use load …

• VPC Endpoints, Transit Gateway and Hybrid Networking

  … TGW --- V3[VPC shared services] TGW --- VPN[Site-to-Site VPN / Direct Connect] Plan non-overlapping CIDR ranges …

• Debug Latency Like an Investigator

  … Check database lock waits, query plans and connection counts. Correlate the release with changed query shape or concurrency …

• Scaling, Load Balancing & Rate Limiting

  … default for stateless HTTP services. Least-connections is not automatically better: a connection may be idle, and a …

• How a Web Request Works

  … You establish a reliable delivery route → TCP connection. 3. You put the letter in a sealed envelope → TLS …

• Graphs: BFS & DFS

  … stations are connected by lines. Some stations connect to many others; you can often reach a station by …

• Concurrency, Resilience & Distributed Workflows

  … Lease, max runtime, bounded concurrency, graceful stop Service Readiness/liveness, connection-pool limits, trace propagation The goal is …

• L6 Production Debugging Casebook

  … See [connection pooling](./connection-pooling-and-database-pressure). 5. Post-full-GC heap remains at 70% and rises …

• VPC Networking Without the Confusion

  … 10.42.0.0/16 → local local connects VPC addresses. 0.0.0.0/0 is the default …

• AWS Databases: Choose the Right One

  … Store credentials in a secret service rather than source code. Connect from an authorized application host inside the …

• CloudWatch: Know What Your App Is Doing

  … Traces connect the work across services. These signals complement each other. Write a useful structured log Instead of …

• Message Queues & RabbitMQ

  Queues let services hand off work without waiting. Learn producers, consumers, acknowledgements, exchanges, retries and dead-letter queues …

• Capacity Planning, SLOs and Error Budgets

  … an N-instance service should survive one instance, zone or dependency loss where required. - Measure saturation: CPU, connection …

• What Is Apache Kafka?

  … read events as part of a group const consumer = kafka.consumer({ groupId: "email-service" }); await consumer.connect(); await …

• Serverless Architecture

  … Functions as a Service, event triggers, cold starts, pay-per-use pricing, managed backends, and the patterns and …

• Authentication, Authorization & API Security

  … Sessions vs JWT, OAuth 2.0 and OpenID Connect, password storage, and the OWASP risks every backend developer …

• Troubleshooting Playbook

  … is empty Service selector does not match pod labels, or pods are not Ready Connection refused targetPort is …

• Resilience Patterns

  … give each dependency its own limited pool of connections, threads or concurrent calls. A slow recommendations service can …

• Observability and Incident Response

  … Restarting every service obscures evidence and may trigger duplicate work. How to prove it worked Run a fault …

• EC2, Storage and Auto Scaling

  … A security group controls allowed connections. An instance profile connects an IAM role to the instance so software …

• Backend Design Scenarios

  … How do you prevent a double charge?]( 7-a-payment-succeeds-at-the-gateway-but-your-service-times …

• Practical Project: Deploy a Real CRM App on EKS

  … crm-core service account and pod role. - [x] backendenv retrieval succeeds. - [x] RDS PostgreSQL connection succeeds. Still to …

• Kafka Producers

  … 5 }); await producer.connect(); export async function publishOrderPlaced(order) { await producer.send({ topic: "shop.orders.placed", acks: -1 …

• Health Checks and Scaling

  … Your app should stop accepting new requests, finish active requests, close connections, then exit. This works with readiness …

• NestJS Core Concepts

  … doesn't know how the service is built. - One instance: shared connections and caches without global variables. Custom …

• Containers at Scale: ECS Deep Dive and EKS

  … Service-to-service communication - ECS Service Connect gives short DNS names, load balancing, retries and metrics between services …

• Domains, Load Balancers and HTTPS

  … Once the browser learns the endpoint address, it connects to the endpoint. This explains why a correct DNS …

• AWS Security Building Blocks

  … Need AWS service --- --- User sign-up and sign-in Cognito User Pools Passwords, API tokens, connection strings Secrets …

• Services and Ingress: Let Traffic Find Your App

  … Learn Services for internal traffic and Ingress for web traffic. The problem Pods are replaceable. A replacement pod …

• Serverless: Lambda and API Gateway

  … long-running connections, very long jobs, specialized runtime needs, or consistently high work where a service is easier …

• C4 Architecture Diagrams: Context, Container, Component and Code

  … The controller turns the HTTP request into a call to Checkout service . 3. The checkout service coordinates the …

• Node.js and Express

  What Node.js is and how it serves thousands of connections on one thread, then Express step by …

• Database Relations & Foreign Keys

  … foreign keys connect one-to-one, one-to-many and many-to-many records](/img/database/relations.svg …

• SOLID at a Glance

  … the socket, not the power plant. How they connect mermaid flowchart TB S["S — one job per class …

• Kubernetes Cluster Architecture, Simply

  … Lets pods talk to each other and lets Services route traffic You do not SSH into a node …

• Clean Error Handling

  … await saveOrder(order); } catch (error) { if (error instanceof ConnectionError) return queueForRetry(order); throw error; // …otherwise let it travel …

• Monolith vs Microservices

  … So design team boundaries and service boundaries together: one team owns a few services end to end (the …

• REST vs GraphQL vs gRPC

  Three popular ways for services to talk. See how each works, compare them side by side, and learn …