Amazon Web Services (AWS) : Placement Groups

In this blog, I am going to discuss an important new features which AWS has released which is called as placement groups. 

So, what are placement groups.
Placement groups are basically directives given to AWS Kernel to place your EC2 instances at specific locations. 
And what are these locations
- specific AZ
- specific RAC
- Zone based
and etc

So, As of now (Sep -2019), AWS has come up with 3 types of placement groups 

1. Cluster
2. Spread
3. Groups

Let's see what is what 

Cluster - Cluster Placement Group is basically a directive to launch EC2 instances within the same Rack.

Visualize thousands of servers placed in Amazon Data Centers and they are placed in different racks, so when you give 'Cluster' as placement group, all the instances will be launched within the same RAC (in same AZ).

Pros 

1. Great in terms of networking (10Gbps between 2 instances)
2. Gives low latency and high n/w throughput
3. Jobs such as Big data benefit 

Cons 
There is one big issue, if the RAC fails, you loose all the instances. 

Spread
Now visualize within all the data centers and you want to distribute your highly available application within multiple data centers, so spread helps you with that - with instances spanning multiple AZs and different physical RAC if in the same AZ.

Pros 

1. Reduced Risk in terms of failure
2. All the instances are on different physical hardware 
3. Provides High Availability for critical applications

Cons

1. You are limited to 7 instances per AZ per placement group. 

Partition

Within one AZ , span  multiple partitions, and what is partition, an isolation created by AWS in their data centers which is a physical boundary and ensures one partition's availability does not affects others. 

Pros

1. Instances do not share racks with other instances
2. Safe from partition failure
3. EC2 instance get access to partition information as metadata
4. Can spawn 100s of instances

Cons

1. The limitation put by AWS (as of now) is 7 partitions per AZ