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A security group acts as a virtual firewall that controls the traffic for one or more instances. When you launch an instance, you associate one or more security groups with the instance. To decide whether to allow traffic to reach an instance, AWS evaluate all the rules from all the security groups that are associated with the instance.

Security groups are not just limited to EC2, but can be used with other services such as RDS.

A DynamoDB stream contains information about both the previous value and the changed value of the item (as applicable). The stream also includes the change type (INSERT, REMOVE, and MODIFY) and the primary key for the item that changed.

Each stream record represents a single data modification in the DynamoDB table to which the stream belongs. Each stream record is assigned a sequence number, reflecting the order in which the record was published to the stream.

DynamoDB Streams provides a time-ordered sequence of item-level changes made to data in a table in the last 24 hours.

You can access a stream with a simple API call and update other data stores or take actions based on the changes made to your table.

Developers could also use DynamoDB Streams to keep data warehousing tools, such as Redshift, in sync for real-time analytics.

EC2 instances belong to different  instance types families and understanding them will help you chose the right instance for your use case. AWS currently have below categories and instance types.

1. General Purpose -  T2, M5, M4, M3

2. Compute Optimized - C5, C4, C3

3. Memory Optimized - X1e, X1, R4, R3

4. Accelerated Computing / Graphics - P3, P2, G3, F1

5. Storage Optimized - H1, I3, D2

EC2 instance type descriptions

1. T2

Amazon Elastic Compute Cloud (EC2) instances are virtual computers on cloud, on which you can install and run applications. 

EC2 has very flexible pricing policies. We can launch servers with applications when needed without upfront commitments, thus eliminating the need to invest in hardware up front and reducing need to forecast. There are also options to reserve servers and get discounts and guarantee.

Using AssumeRoleWithWebIdentity API you can authenticate users using web identity providers such as Amazon, Google, Facebook or any other open-id compatible identity provider.

Following steps need to be completed first:

1. Go to IAM

2. Click on Create New Role

3. Select Role for identity provider access

4. Select grant access to identity providers