Merge pull request open-guides#116 from mkulke/alb-gotcha

Added ALB Gotcha about unhealthy targets (Attempt open-guides#2)

README.md

@@ -880,6 +880,7 @@ ALB
 -	ALBs do not (yet) 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.
 
 Elastic IPs
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