azGateways

What are some different gateways?

Load balancer

• pretty dumb
• works at TCP/UDP level
• passes data on but never looks at it
• used to load balance on the transport layer (layer 4 eg: 192.168.0.1:8080 -> backend pool 1)
• NAT for public access
• preserves source IP and details
• acts more like a switch by not interacting with the payloads
• test health with health probes and pull bad nodes out of cycle

Traffic Manager

• load balancer at a global level
• layer 4 (IP, ports etc)
• evenly distributes the load
• routes but does not interact with the data passing through (so no termination or handoff)
• load balances virtual machines
• can route over microsoft network

Application Gateway

• used to load balance on the application layer (layer 7 eg: /api/videos -> backend pool 1, /web/images/ -> backend pool 2).
• single point of contact acting like a reverse proxy routing traffic to back end pools
• single point of contact (ip address) can host 100 domain names and route requests based on domain name
• global version of an application gateway
• application gateway can not work cross region as it resides in a vnet
  • layer 7 (http)
  • (supports) TLS termination but supports end to end tls (?)
  • web application firewall capability
  • protects against OWASP vulnerabilities
  • load balancing capability
  • vnet integration
  • logging
  • supports handoff and termination
  • no support for authentication which must be managed by backend pool
  • promotes availability
  • supports scalability/elasticity
  • route over microsoft network

API Gateway

• azure doesn't have a dedicated one - it is wrapped up in APIM
• secure and scale APIs
• orchestrator between requests and backend services (map/reduce)

Azure specific gateways

API Management Service

• layer 7
• three parts
  • api gateway
  • admin portal
  • developer portal
• NO load balancing
• self - hosted gateways allow local transport routing - but requires agents installed on backend
• modify requests
• modify responses
• routing to backend
• quota management (rate limiting)
• caching
• validate jwt
• authn and authz
• black/white list IPs

Front door/application gateway (application layer 7)

• intelligent
• works at HTTP/HTTPS level
• can hand off ssl and make routing decisions based on data

Azure Front Door vs Azure Traffic Manager

• Front Door is to Traffic Manager what Application Gateway is to Load Balancer
• both are layer 7

What is DNS routing

• doesn't see the traffic
• works with DNS requests from the client to redirect traffic
• helps client determine which IP address to resolve to based on rules

Examples of software api gateways: nginx, HAProxy, Ocelot (.net core native)

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