Private vs Public vs Elastic IP

Private vs Public IP

Networking has two sorts of IPs. IPv4 and IPv6

Elastic IP

When you stop and start an EC2 instance, it can change its public IP. If you need to have a fixed public IP for your instance, you need an Elastic IP. An Elastic IP is a public IPv4 IIP you own as long as you don’t delete it.

• Can attach to one instance at a type

• Can mask failure of an instance by rapidly remapping address to another instance

• Max 5 unless asked for

• Try to avoid using an Elastic IP:

  • Often reflect poor architectural decisions
  • Use a random public IP and register a DNS name to it
  • Or use a Load Balancer

  Placement Groups

  Control over the EC2 instance placement strategy. Defined using placement groups. When you create a placement group, you specify one of the following strategies for the group:

  • Cluster - cluster instances into a low-latency group in a single AZ
  • Spread - spreads instances across underlying hardware (max 7 instances per group per AZ) critical applications
  • Partition - spreads instances across many different partitions (which rely on different set of racks) within an AZ. Scales to 100s of EC2 instances per group (Hadoop, Cassandra, Kafka)