Microservices give you flexibility and speed. But each service is also an attack surface. Security in a distributed system is harder than in a monolith because there are more moving parts and more places things can go wrong.
Here's what I focus on when securing microservices on Azure.
The main threats
Injection attacks: Services communicate through APIs. SQL injection, command injection, and similar attacks target those endpoints. Validate every input. Put an API gateway in front of your services to centralize that enforcement.
Broken access control: Each service needs its own identity and permissions. Use OAuth 2.0 for consistent access control. Follow least privilege: each service only gets access to what it actually needs.
Data interception: Data moving between services can be intercepted or tampered with. Enforce TLS for all inter-service communication. Store cryptographic keys in Azure Key Vault, not in config files or environment variables.
DDoS: Distributed systems can amplify DDoS impact. One service going down can cascade. Use rate limiting, traffic shaping, and Azure DDoS Protection. Autoscaling helps absorb traffic spikes.
Azure tools that help
AKS security: Azure Kubernetes Service has network policies, RBAC, and Azure Policy integration. Use them. Don't run containers with elevated privileges unless you have a specific reason.
Azure API Management: Centralizes authentication, authorization, rate limiting, and analytics for your APIs. Gives you visibility into usage patterns and helps catch anomalies.
Application Gateway WAF: The Web Application Firewall blocks common attacks like SQL injection, XSS, and CSRF before they reach your services. Put it in front of public-facing services.
Azure Monitor and Defender for Cloud: Aggregate telemetry across your stack. Set up alerts. Act on Defender's recommendations rather than treating them as optional.
Development practices
Container security: Scan images in Azure Container Registry before deployment. Run with minimal permissions. Use AKS admission controllers to enforce runtime policies.
Immutable infrastructure: Define infrastructure in code using Terraform or ARM templates. Use blue-green or canary deployments to reduce exposure when releasing changes.
DevSecOps: Security checks belong in the CI/CD pipeline. Automated scanning, dependency vulnerability checks, and security gates before merge catch issues early. Fixing a vulnerability before it ships is orders of magnitude cheaper than patching it in production.
Security is not a feature you add at the end. In microservices, it has to be built into every layer from day one.