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Merge pull request #477 from open-guides/alb-routing-capabilities-cleanup

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Clean up ALB routing capability information
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Corey Quinn 2017-08-15 13:11:59 -07:00 committed by GitHub
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@ -1060,14 +1060,13 @@ ALB
### ALB Tips
- Use ALBs to route to services that are hosted on shared clusters with dynamic port assignment (like ECS or Mesos).
- ALBs support HTTP path-based routing (send HTTP requests for “/api/*” -> {target-group-1}, “/blog/*” -> {target group 2}).
- ALBs support [HTTP host-based routing](http://docs.aws.amazon.com/elasticloadbalancing/latest/application/load-balancer-listeners.html#host-conditions) (send HTTP requests for “api.mydomain.com” -> {target-group-1}, “blog.mydomain.com” -> {target group 2}) as well as [HTTP path-based routing](http://docs.aws.amazon.com/elasticloadbalancing/latest/application/load-balancer-listeners.html#path-conditions) (send HTTP requests for “/api/*” -> {target-group-1}, “/blog/*” -> {target group 2}).
### ALB Gotchas and Limitations
- 🔸ALBs only support HTTP/2 over HTTPS (no plain-text HTTP/2).
- 🔸ALBs only support HTTP/2 to external clients and not to internal resources (instances/containers).
- ALBs support HTTP routing but not port-based TCP routing.
- ALBs support routing based on HTTP “Host” header or HTTP verb
- Instances in the ALB’s target groups have to either have a single, fixed healthcheck port (“EC2 instance”-level healthcheck) or the healthcheck port for a target has to be the same as its application port (“Application instance”-level healthcheck) - you can't configure a per-target healthcheck port that is different than the application port.
- ALBs are VPC-only (they are not available in EC2 Classic)
- In a target group, if there is no healthy target, all requests are routed to all targets. For example, if you point a listener at a target group containing a single service that has a long initialization phase (during which the health checks would fail), requests will reach the service while it is still starting up.