Reliable crypto transactions at Coinbase

Ryland Goldstein

Ryland Goldstein

Head of Product

Link to PDF version

This case study is based on an interview with Anthony Dmitriyev who was a key player in Temporal* adoption within Coinbase

Coinbase’s mission is to create an open financial system for the world. Finding a solution which allows you to innovate without additional risk is critical and why Coinbase began re-architecting their core transaction workload.

Problem:

Coinbase processes millions of cryptocurrency transactions every day. From their users point of view, each transaction is reduced to a binary result of "succeeded" or "failed". Under the hood each of these transactions consists of a series of steps. A simplified example of a transactions steps might be:

  1. Withdraw foocoin from user A's wallet
  2. Withdraw barcoin from user B's wallet
  3. Deposit foocoin into user B's wallet
  4. Deposit barcoin into user A's wallet

If all of these steps succeed, the user-level transaction succeeds. On the other hand, if a step fails the user-level transaction cannot fail until the steps which were already executed are rolled back. This need to rollback is traditionally accomplished using SAGA - a common pattern for handling rollbacks in distributed transactions.

Until recently Coinbase relied on a custom engine to handle these SAGA needs. The homegrown system was quite reliable and well-suited enough for SAGA support, but when teams began trying to extend the system to be useful in other domains things became painful. Each new use case the system needed to support translated into a large amount of plumbing and developer work. Coinbase quickly realized that they were going to need a flexible, general-purpose solution if they wanted to continue scaling and innovating.

Searching for Answers:

A search began for a replacement to their homegrown system. The most important feature was the ability to support the existing SAGA patterns which constitute the bread and butter of Coinbase's business. The contenders were quickly narrowed down to 3 finalists:

  • Zeebe
  • AWS Step Functions
  • Temporal/Cadence

SAGA workflows were built on each of the contending platforms. In the process, the team realized that both the Zeebe and Step Functions development models forced users to predefine all of their possible execution paths upfront. This is a real problem in the context of SAGAS, since compensation logic is required for each step which can potentially fail. With Zeebe and Step Functions this meant that each step required one or more prebuilt DAGs to handle the potential failures. If your SAGAS consist of a few simple steps, prebuilding DAGs might be feasible, but as complexity increases the overhead becomes enormous.

Trying to model complex SAGAS using a plain execution graph such as Zeebe and Step Functions provide will make things unnecessarily more complex, plus we want a solution which we could explore for more use cases that don't necessarily use SAGAS. So I think this is where Temporal* really shined.

Fortunately Temporal did not come with these drawbacks. Instead of requiring the user to define each possible path upfront using unfriendly DAGs, Temporal enables users to handle failures programmatically. Not only did this make things more manageable, it became possible to share and reuse logic that would have otherwise been isolated.

Temporal* allows us to do SAGAS easily, but is also deep and very extendable.

A slow transformation

When running sensitive workloads at Coinbase scale, it's generally not a great idea to migrate your entire system at once. So once the decision was made to move forward with Temporal, a migration strategy was needed that would enable Coinbase to incrementally shift their critical transaction workload. The team began iteratively replacing each existing component with a Temporal workflow. They relied on Coinbase's open source deployment system to build containers for each of the translated workflows and make them available via blue/green deployments. Each new workflow was put behind a feature flag until it had been running long enough for the team to feel confident putting it center stage. Before long, the majority of existing workflows had been successfully migrated to Temporal*.

For every specific use case we migrated we used a very incremental process. We would take a single use case and translate it to be a Temporal* workflow. Then we would put it behind feature flag and do a progressive rollout.

Retrospect:

Temporal maintains the high level of reliability offered by the homegrown system while also providing tremendous amounts of visibility into running processes.
Temporal* brings a lot of visibility into what is happening which was not something we had with our previous system.

Development velocity has also increased as developers can focus exclusively on writing code instead of maintaining a homegrown SAGA solution. Temporal* has opened up use cases which weren't even imaginable with the homegrown system.

Temporal* opened up a lot of possibilities of what we could do with the system.

Things that seemed complex before don't really seem that way anymore.

Things that we thought to be much more complex to implement on top of the old system feel like they are much easier with Temporal*.
*As of the time of writing this article Coinbase is using Cadence (the Temporal predecessor) and is only evaluating a future migration to Temporal