Membership and Failure Detection in DynamoDB: An Inside Look Into NoSQL, Part 7

This is a guest post from 47Line Technologies.

In our previous post, How to handle failures in DynamoDB – An inside look into NoSQL, we discussed handling failures via Hinted Handoff & Replica Synchronization. We also talked about the advantages of using a Sloppy Quorum and Merkle Trees.

In this last & final part of the series, we will look into Membership and Failure Detection.

Ring Membership

In any production environment, node outages are often transient. But it rarely signifies permanent failure and hence there is no need for repair or rebalancing the partition. On the other hand, manual errors might result in the unintentional startup of new DynamoDB nodes. A proper mechanism is essential for the addition and removal of nodes from the DynamoDB Ring. An administrator uses a tool to issue a membership change command to either add/remove a node. The node that picks up this request writes into its persistent store the membership change request and the timestamp.

A gossip-based protocol transfers the membership changes and maintains a consistent view of membership across all nodes. Each node contacts a peer chosen at random every second and the two nodes efficiently reconcile their persisted membership change histories. Partitioning & placement information also propagates via the gossip-based protocol and each storage node is aware of the token ranges its peers are responsible for. This allows each node to forward a key’s read/write operations to the right set of nodes directly.

Ring Membership (Credit)

External Discovery

It’s best to explain with an example: An administrator joins node A to the ring. He then joins node B to the ring. Nodes A and B consider itself as part of the ring, yet neither would be immediately aware of each other. To prevent these logical partitions, DynamoDB introduced the concept of seed nodes. Seed nodes are fully functional nodes that are discovered via an external mechanism (static configuration or a configuration service) and are known to all nodes. Since each node communicates with the seed node and gossip-based protocol transfer the membership changes, logical partitions are highly unlikely.

Failure Detection

Failure detection in DynamoDB is used to avoid attempts to communicate with unreachable peers during get() and put() operations and when transferring partitions and hinted replicas. For the purpose of avoiding failed attempts at communication, a purely local notion of failure detection is entirely sufficient: node A may consider node B failed if node B does not respond to node A’s messages (even if B is responsive to node C‘s messages). In the presence of a steady rate of client requests generating inter-node communication in the DynamoDB ring, a node A quickly discovers that a node B is unresponsive when B fails to respond to a message; Node A then uses alternate nodes to service requests that map to B‘s partitions; A also periodically retries B to check for the latter’s recovery. In the absence of client requests to drive traffic between two nodes, neither node really needs to know whether the other is reachable and responsive.

Conclusion

This exhaustive 7-part series detailing every component is sufficient to understand the design and architecture of any NoSQL system. Phew! What an incredible journey it has been these couple of months delving into the internals of DynamoDB. Having patiently read this far, you are amongst the chosen few who have this sort of deep NoSQL knowledge. You can be extremely proud of yourself!

Let’s eagerly await another expedition soon!

Article authored by Vijay Olety.

Avatar

Written by

47Line Technologies

47Line is building solutions solving critical business problems using “cloud as the backbone”. The team has been working in Cloud Computing domain for last 6 years and have proven thought leadership in Cloud, Big Data technologies.


Related Posts

Amanda Cross
Amanda Cross
— January 7, 2021

New Content: AWS Terraform, Java Programming Lab Challenges, Azure DP-900 & DP-300 Certification Exam Prep, Plus Plenty More Amazon, Google, Microsoft, and Big Data Courses

This month our Content Team continues building the catalog of courses for everyone learning about AWS, GCP, and Microsoft Azure. In addition, this month’s updates include several Java programming lab challenges and a couple of courses on big data. In total, we released five new learning...

Read more
  • AWS
  • Azure
  • DevOps
  • Google Cloud Platform
  • Machine Learning
  • programming
Avatar
Stuart Scott
— December 17, 2020

Where Should You Be Focusing Your AWS Security Efforts?

Another day, another re:Invent session! This time I listened to Stephen Schmidt’s session, “AWS Security: Where we've been, where we're going.” Amongst covering the highlights of AWS security during 2020, a number of newly added AWS features/services were discussed, including: AWS Audit...

Read more
  • AWS
  • AWS re:Invent
  • cloud security
Joe Nemer
Joe Nemer
— December 4, 2020

AWS re:Invent: 2020 Keynote Top Highlights and More

We’ve gotten through the first five days of the special all-virtual 2020 edition of AWS re:Invent. It’s always a really exciting time for practitioners in the field to see what features and services AWS has cooked up for the year ahead.  This year’s conference is a marathon and not a...

Read more
  • AWS
  • AWS Glue Elastic Views
  • AWS re:Invent
Bryony Harrower
Bryony Harrower
— November 6, 2020

WARNING: Great Cloud Content Ahead

At Cloud Academy, content is at the heart of what we do. We work with the world’s leading cloud and operations teams to develop video courses and learning paths that accelerate teams and drive digital transformation. First and foremost, we listen to our customers’ needs and we stay ahea...

Read more
  • AWS
  • Azure
  • content roadmap
  • GCP
Joe Nemer
Joe Nemer
— October 25, 2020

Excelling in AWS, Azure, and Beyond – How Danut Prisacaru Prepares for the Future

Meet Danut Prisacaru. Danut has been a Software Architect for the past 10 years and has been involved in Software Engineering for 30 years. He’s passionate about software and learning, and jokes that coding is basically the only thing he can do well (!). We think his enthusiasm shines t...

Read more
  • AWS
  • careers
  • champions
  • upskilling
Joe Nemer
Joe Nemer
— October 14, 2020

New Content: AWS Data Analytics – Specialty Certification, Azure AI-900 Certification, Plus New Learning Paths, Courses, Labs, and More

This month our Content Team released two big certification Learning Paths: the AWS Certified Data Analytics - Speciality, and the Azure AI Fundamentals AI-900. In total, we released four new Learning Paths, 16 courses, 24 assessments, and 11 labs.  New content on Cloud Academy At any ...

Read more
  • AWS
  • Azure
  • DevOps
  • Google Cloud Platform
  • Machine Learning
  • programming
Joe Nemer
Joe Nemer
— September 15, 2020

New Content: Azure DP-100 Certification, Alibaba Cloud Certified Associate Prep, 13 Security Labs, and Much More

This past month our Content Team served up a heaping spoonful of new and updated content. Not only did our experts release the brand new Azure DP-100 Certification Learning Path, but they also created 18 new hands-on labs — and so much more! New content on Cloud Academy At any time, y...

Read more
  • AWS
  • Azure
  • DevOps
  • Google Cloud Platform
  • Machine Learning
  • programming
Joe Nemer
Joe Nemer
— August 28, 2020

AWS Certification Practice Exam: What to Expect from Test Questions

If you’re building applications on the AWS cloud or looking to get started in cloud computing, certification is a way to build deep knowledge in key services unique to the AWS platform. AWS currently offers 12 certifications that cover major cloud roles including Solutions Architect, De...

Read more
  • AWS
  • AWS Certifications
Patrick Navarro
Patrick Navarro
— August 25, 2020

Overcoming Unprecedented Business Challenges with AWS

From auto-scaling applications with high availability to video conferencing that’s used by everyone, every day —  cloud technology has never been more popular or in-demand. But what does this mean for experienced cloud professionals and the challenges they face as they carve out a new p...

Read more
  • AWS
  • Cloud Adoption
  • digital transformation
Avatar
Andrew Larkin
— August 18, 2020

Constant Content: Cloud Academy’s Q3 2020 Roadmap

Hello —  Andy Larkin here, VP of Content at Cloud Academy. I am pleased to release our roadmap for the next three months of 2020 — August through October. Let me walk you through the content we have planned for you and how this content can help you gain skills, get certified, and...

Read more
  • alibaba
  • AWS
  • Azure
  • content roadmap
  • Content updates
  • DevOps
  • GCP
  • Google Cloud
  • New content
Alisha Reyes
Alisha Reyes
— August 5, 2020

New Content: Alibaba, Azure AZ-303 and AZ-304, Site Reliability Engineering (SRE) Foundation, Python 3 Programming, 16 Hands-on Labs, and Much More

This month our Content Team did an amazing job at publishing and updating a ton of new content. Not only did our experts release the brand new AZ-303 and AZ-304 Certification Learning Paths, but they also created 16 new hands-on labs — and so much more! New content on Cloud Academy At...

Read more
  • AWS
  • Azure
  • DevOps
  • Google Cloud Platform
  • Machine Learning
  • programming
Alisha Reyes
Alisha Reyes
— July 16, 2020

Blog Digest: Which Certifications Should I Get?, The 12 Microsoft Azure Certifications, 6 Ways to Prevent a Data Breach, and More

This month, we were excited to announce that Cloud Academy was recognized in the G2 Summer 2020 reports! These reports highlight the top-rated solutions in the industry, as chosen by the source that matters most: customers. We're grateful to have been nominated as a High Performer in se...

Read more
  • AWS
  • Azure
  • blog digest
  • Certifications
  • Cloud Academy
  • OWASP
  • OWASP Top 10
  • Security
  • VPCs