AWS HA : Plan for Failure

Load Balancers:

ALB: Application Load balancer, http/https traffic operate at layer 7.It has intelligent routing. Sticky session added to target Group level.

NLB : Network load balancer, Load balancing for TCP traffic, operates at connection level. Operate at connection level 4. Maintains ultra low-latency serves millions of reqs/sec

Classic Load balancers :Basic one most cost effective, simple routing. . http/https, operates at layer 7. Supports x-forwarded, sticky session, layer 4 balancing of app that rely on TCP protocol.

504 error , gateway has timed out  when application fails to respond within the ideal timeout period.

X-Forwarded-For header helps know the original IP the client request has come from.. client IP -> ELB- > Web server.

Load Balancers have their DNS names and never given an IP address.

-When you are writing to disk or storing information , sticky session would be useful to have access to the file system.

Cross Zone Load Balancing:

Az1 -50%(EC1, EC2, EC3, EC4)/ Az250%( (EC5)-à 20%,20%,20%,20%,20%

Path based routing:  /images ->target(ua-east AZ) group2  . /services -> target group1 (West AZ)

Multi-AZs for disaster recovery and Read Replicas for performance

Scaling out: increase more EC2 instances, Scale up : increase the resources

Standard S3 and Standatd IA are still highly available . Not highly available : RRS and IA -SZ

-ELB do not have predefined IPs. It resolves by DNS name.

-Alias name is going to use to point to EC2 not the cname.

The ALB has functionality to distinguish traffic for different targets (mysite.co/accounts vs. mysite.co/sales vs. mysite.co/support) and distribute traffic based on rules for target group, condition, and priority.

Pilot Light: critical applications and data at the ready so that it can be quickly retrieved if needed.

Warm Standby:  duplicate version of your business’ core elements running on standby at all times, which makes for a little downtime and an almost seamless transition.