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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

Throughput and Pricing Example 1 (from Amazon docs)

Your application needs to perform 5 million writes and 5 million eventually consistent reads per day on a DynamoDB table, while storing 8 GB of data. Items are no larger than 1 KB in size. 

Pricing: $0.47 per WCU per month, At $0.09 per RCU per month, $0.25 per GB per month.

Write Capacity Units (WCUs)

= 5 million writes per day

= 57.9 writes per second.

1 WCU can handle 1 write per second, so you need 58 WCUs.

At $0.47 per WCU per month, 58 WCUs costs $27.26 per month.

DynamoDB throughput provisioning might look bit difficult to understand and hence adding examples.

Throughput Provisioning - Basic Concepts

Provisioned Throughput (Write)

• One write capacity unit (WCU) provides up to one write per second

• Enough for 2.5 million writes per month               

• Price as low as  $0.47 per WCU

Pay only for the resources you provision.

You do not allocate memory, CPU, and other system resources. Instead you specify the target utilization rate and minimum to maximum capacity that you want for your table.

DynamoDB handles the provisioning of resources to achieve your target utilization of read and write capacity, and also auto scales your capacity based on usage. 

Optionally, you can directly specify read and write capacity if you prefer to manually manage table throughput.