This post was co-written with Brian Nutt, Senior Software Engineer and Kao Makino, Principal Performance Engineer, both at Snowflake.

Transactional databases are a key component of any production system. Maintaining data integrity while rows are read and written at a massive scale is a major technical challenge for these types of databases. To ensure their stability, it’s necessary to test many different scenarios and configurations. Simulating as many of these as possible allows engineers to quickly catch defects and build resilience. But the Holy Grail is to accomplish this at scale and within a timeframe that allows your developers to iterate quickly.

Snowflake has been using and advancing FoundationDB (FDB), an open-source, ACID-compliant, distributed key-value store since 2014. FDB, running on Amazon Elastic Cloud Compute (EC2) and Amazon Elastic Block Storage (EBS), has proven to be extremely reliable and is a key part of Snowflake’s cloud services layer architecture. To support its development process of creating high quality and stable software, Snowflake developed Project Joshua, an internal system that leverages Amazon Elastic Kubernetes Service (EKS), Amazon Elastic Container Registry (ECR), Amazon EC2 Spot Instances, and AWS PrivateLink to run over one hundred thousand of validation and regression tests an hour.

About Snowflake

Snowflake is a single, integrated data platform delivered as a service. Built from the ground up for the cloud, Snowflake’s unique multi-cluster shared data architecture delivers the performance, scale, elasticity, and concurrency that today’s organizations require. It features storage, compute, and global services layers that are physically separated but logically integrated. Data workloads scale independently from one another, making it an ideal platform for data warehousing, data lakes, data engineering, data science, modern data sharing, and developing data applications.

Snowflake architecture

Developing a simulation-based testing and validation framework

Snowflake’s cloud services layer is composed of a collection of services that manage virtual warehouses, query optimization, and transactions. This layer relies on rich metadata stored in FDB.

Prior to the creation of the simulation framework, Project Joshua, FDB developers ran tests on their laptops and were limited by the number they could run. Additionally, there was a scheduled nightly job for running further tests.

Joshua at Snowflake

Amazon EKS as the foundation

Snowflake’s platform team decided to use Kubernetes to build Project Joshua. Their focus was on helping engineers run their workloads instead of spending cycles on the management of the control plane. They turned to Amazon EKS to achieve their scalability needs. This was a crucial success criterion for Project Joshua since at any point in time there could be hundreds of nodes running in the cluster. Snowflake utilizes the Kubernetes Cluster Autoscaler to dynamically scale worker nodes in minutes to support a tests-based queue of Joshua’s requests.

With the integration of Amazon EKS and Amazon Virtual Private Cloud (Amazon VPC), Snowflake is able to control access to the required resources. For example: the database that serves Joshua’s test queues is external to the EKS cluster. By using the Amazon VPC CNI plugin, each pod receives an IP address in the VPC and Snowflake can control access to the test queue via security groups.

To achieve its desired performance, Snowflake created its own custom pod scaler, which responds quicker to changes than using a custom metric for pod scheduling.

  • The agent scaler is responsible for monitoring a test queue in the coordination database (which, coincidentally, is also FDB) to schedule Joshua agents. The agent scaler communicates directly with Amazon EKS using the Kubernetes API to schedule tests in parallel.
  • Joshua agents (one agent per pod) are responsible for pulling tests from the test queue, executing, and reporting results. Tests are run one at a time within the EKS Cluster until the test queue is drained.

Achieving scale and cost savings with Amazon EC2 Spot

A Spot Fleet is a collection—or fleet—of Amazon EC2 Spot instances that Joshua uses to make the infrastructure more reliable and cost effective. ​ Spot Fleet is used to reduce the cost of worker nodes by running a variety of instance types.

With Spot Fleet, Snowflake requests a combination of different instance types to help ensure that demand gets fulfilled. These options make Fleet more tolerant of surges in demand for instance types. If a surge occurs it will not significantly affect tasks since Joshua is agnostic to the type of instance and can fall back to a different instance type and still be available.

For reservations, Snowflake uses the capacity-optimized allocation strategy to automatically launch Spot Instances into the most available pools by looking at real-time capacity data and predicting which are the most available. This helps Snowflake quickly switch instances reserved to what is most available in the Spot market, instead of spending time contending for the cheapest instances, at the cost of a potentially higher price.

Overcoming hurdles

Snowflake’s usage of a public container registry posed a scalability challenge. When starting hundreds of worker nodes, each node needs to pull images from the public registry. This can lead to a potential rate limiting issue when all outbound traffic goes through a NAT gateway.

For example, consider 1,000 nodes pulling a 10 GB image. Each pull request requires each node to download the image across the public internet. Some issues that need to be addressed are latency, reliability, and increased costs due to the additional time to download an image for each test. Also, container registries can become unavailable or may rate-limit download requests. Lastly, images are pulled through public internet and other services in the cluster can experience pulling issues.

​For anything more than a minimal workload, a local container registry is needed. If an image is first pulled from the public registry and then pushed to a local registry (cache), it only needs to pull once from the public registry, then all worker nodes benefit from a local pull. That’s why Snowflake decided to replicate images to ECR, a fully managed docker container registry, providing a reliable local registry to store images. Additional benefits for the local registry are that it’s not exclusive to Joshua; all platform components required for Snowflake clusters can be cached in the local ECR Registry. For additional security and performance Snowflake uses AWS PrivateLink to keep all network traffic from ECR to the workers nodes within the AWS network. It also resolved rate-limiting issues from pulling images from a public registry with unauthenticated requests, unblocking other cluster nodes from pulling critical images for operation.

Conclusion

Project Joshua allows Snowflake to enable developers to test more scenarios without having to worry about the management of the infrastructure. ​ Snowflake’s engineers can schedule thousands of test simulations and configurations to catch bugs faster. FDB is a key component of ​the Snowflake stack and Project Joshua helps make FDB more stable and resilient. Additionally, Amazon EC2 Spot has provided non-trivial cost savings to Snowflake vs. running on-demand or buying reserved instances.

If you want to know more about how Snowflake built its high performance data warehouse as a Service on AWS, watch the This is My Architecture video below.