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What is a Custom metric? You can create a custom metric (script) from your EC2 instance and monitor that metric by pushing it to CloudWatch. How to push your metric to CloudWatch? $ crontab -e $ crontab -e Add the following line to execute your script every minute: */1 * * * * /home/ec2-user/mem.sh Save and exit.

NAT Gateways are more suitable for higher bandwidth requirements than NAT Instance (scales up to 45Gbps). Whereas, NAT Instances depend on bandwidth of instance types Zone independent architecture - Create NAT Gateways in each AZ. This ensures high availability. Whereas in NAT Instances, we have to manage failover between instances using scripts Can we replace NAT Gateways/NAT Instances with a VPN connection? No. VPNs are used to connect to route traffic in a private network (skipping Internet). NAT Gateways/NAT Instances are used to route traffic from EC2 instances in the private subnet to Internet.

You would have heard the word elasticity multiple times in AWS. What does it mean? Suppose you have an EC2 instance. After the load increases, it would be better if there is another EC2 instance to share the load. So, you launch another instance through Auto-Scaling. Now, the load is shared by these two instances. The EC2 instances, since one can do the same work of the other, are elastic . This is called as elasticity .