Emails service with support for enqueue jobs

[kamilkisiela]

Emails service with support for enqueue jobs

[kamilkisiela]

Types of emails we need (as of today)

• Notify org's owner about reaching 90% of the usage limit
• Notify org's owner about the rate-limit
• Notify org's owner about the upcoming end of the trial period

Scheduling

I think the "upcoming end of the trial" email could be sent from Stripe directly.

The first two emails (related to usage limits) should be scheduled by either the usage-estimator or the rate-limit service but only if the email hasn't been scheduled yet (within the billing period).

Instead of holding the state (email sent or not yet) in Postgres, the email service could use BullMQ (Redis) with specific job names (rate-limit-org{id}-period{currentPeriod}).
The problem with this approach is the persistence of data (Redis is in-memory) that can cause sending multiple emails. The data is gone when the pod is restarted (version upgrade of Redis or K8s). We would have to use external storage.

Rendering emails

Who should create an email body?
Should it be done in the email service (data + template id) or by the consumer (email prepared by rate-limit service)?
Doing it in the email service means it is aware of all the email templates but on the other hand, who cares? Making everything isolated just to make it isolated makes no sense.

How should the body be created?
We need simple HTML with a few CSS rules.

Maybe a type-safe template?

const email = getEmail('template-name-here');
//                           ^ type-safe: to make sure the template exists
const body = email.body({ ...props });
//                         ^ type-safe: to make sure we pass all the data
const title = email.title({ ...props });
//                           ^ type-safe: to make sure we pass all the data

Maybe a combination of TypeScript and mjml? It has an online editor and a big community and a big list of features.

We could have an "email client" that is fully type-safe, holds all the email templates, and connects to the email service nicely. Keeping the emails in a single place is fine. We could use tRPC here.

emailService.send({
  template: 'rate-limit',
  address: '[email protected]',
  input: {
    org: { name: 'GraphQL Hive' },
    limit: 1_000_000,
    used: 1_100_000,
  }
});