Exam AWS Certified Solutions Architect - Professional SAP-C02 topic 1 question 150 discussion

3 nodes are required for a DAX cluster to be fault-tolerant. https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/DAX.concepts.cluster.html

This is a poorly framed question with very little attention to how applications are architected in real life. Here's my reasoning: This being a trading platform, you have a high volume of writes and reads, and stale data is essentially worse than useless. This automatically eliminates all but A, because of the way DAX performs. DAX caches data from the first query, and subsequent queries will continue to receive that cached data regardless of whether it has been updated in DynamoDB. This behavior continues till cache eviction. The only way around it is to read and write data using DAX. Here's the curveball - the solution must be HA, which eliminates A and D, leaving only B & C. And between B & C, you really want to use DAX for reading and DynamoDB for writing. So final answer is B - if you want to get certified. Applying this solution in real world however will cause you a lot of pain and grief!

B is Correct. - To achieve high availability for your application, we recommend that you provision your DAX cluster with at least three nodes. Ref: https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/DAX.consistency.html#DAX.consistency.nodes - If the request specifies eventually consistent reads (the default behavior), it tries to read the item from DAX. - With these operations, data is first written to the DynamoDB table, and then to the DAX cluster. The operation is successful only if the data is successfully written to both the table and to DAX. Ref: https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/DAX.concepts.html#DAX.concepts.request-processing

DAX is cache and can only be used to read so A and C are out. Between B and D the question says Highly Available so we will select B (three node) instead of D (single node). So correct answer B

A = 2 nodes DAX is not fault-tolerant B = correct (write-around strategy ensure lower latency) C = write-through strategy can have higher latency D = 1 node DAX is not fault-tolerant

Option B is the best option. Though Option A is also possible solution.

The breakpoint is latency. You write throught DAX, but for latency sensitive apps, AWS instruct write directly on DynamoDB instead on DAX. "For applications that are sensitive to latency, writing through DAX incurs an extra network hop. So a write to DAX is a little slower than a write directly to DynamoDB. If your application is sensitive to write latency, you can reduce the latency by writing directly to DynamoDB instead. For more information, see Write-around." https://docs.aws.amazon.com/amazondynamodb/latest/developerguide/DAX.consistency.html#DAX.consistency.strategies-for-writes

Option A would be the least latency solution for this use case. Using a two node DAX cluster with the application reading and writing via DAX provides: Caching of both reads and writes within the DAX cluster nodes. This eliminates the need to go directly to DynamoDB for reads and writes, reducing latency. Redundancy with two nodes to ensure high availability of the cache. The other options would lead to some reads or writes still going directly to DynamoDB rather than being fully served from the lower latency cached data in DAX. This could increase latency compared to option A. A single node DAX cluster would work but lacks the redundancy needed for high availability. DAX is fully managed, in-memory cache for DynamoDB that delivers low-latency data access. By caching the entire dataset in-memory across nodes, it can serve requests much faster than going to the DynamoDB tables on every request. The AWS documentation provides more details on how to configure DAX and monitor latency metrics.

Question only ask for High Availability, not Fault Tolerant. You need 3 nodes only for the latter. You must write through to keep data getting stale as mentioned by Ganshank. I would go with two-node cluster as strong consistency adds extra latency as number of clusters increase. So for this question best answer should be A.

Option B is correct: DAX is also used for caching so it improves the performance and for production 3 nodes are strongly recommended so i ll go with B.

https://aws.amazon.com/blogs/database/amazon-dynamodb-accelerator-dax-a-read-throughwrite-through-cache-for-dynamodb/

sorry guys a is wrong ans: B is correct ans Important For production usage, we strongly recommend using DAX with at least three nodes, where each node is placed in different Availability Zones. Three nodes are required for a DAX cluster to be fault-tolerant. A DAX cluster can be deployed with one or two nodes for development or test workloads. One- and two-node clusters are not fault-tolerant, and we don't recommend using fewer than three nodes for production use. If a one- or two-node cluster encounters software or hardware errors, the cluster can become unavailable or lose cached data.

A is Ans : Read replicas serve two additional purposes: Scalability. If you have a large number of application clients that need to access DAX concurrently, you can add more replicas for read-scaling. DAX spreads the load evenly across all the nodes in the cluster. (Another way to increase throughput is to use larger cache node types.) High availability. In the event of a primary node failure, DAX automatically fails over to a read replica and designates it as the new primary. If a replica node fails, other nodes in the DAX cluster can still serve requests until the failed node can be recovered. For maximum fault tolerance, you should deploy read replicas in separate Availability Zones. This configuration ensures that your DAX cluster can continue to function, even if an entire Availability Zone becomes unavailable.

A Once u enable DAX you cant directly write onto or Read from Dynamo DB.

Correct B.

AWS recommend 3 nodes for production workloads. So it must B

B for DAX HA