PostHog

Capture logs as PostHog events linked to persons

Send logs to PostHog as captured events. Each log becomes an event with dot-notation properties you can use in filters, insights, and cohorts — and logs carrying a user ID link to PostHog persons automatically.

Setup

Copy your project API key (phc_…) from Settings → Project → Project API Key.
Set the environment variables:

POSTHOG_API_KEY=phc_your-project-key
POSTHOG_HOST=https://us.i.posthog.com # or https://eu.i.posthog.com

Wire the transport:

import { Elysia } from 'elysia'
import logixlysia from 'logixlysia'
import { createPostHogTransport } from 'logixlysia/posthog'

const app = new Elysia()
  .use(
    logixlysia({
      config: {
        transports: [createPostHogTransport()]
      }
    })
  )
  .get('/', () => 'ok')
  .listen(3000)

Trigger a request and find logixlysia_log events in the activity explorer.

Environment Variables

Variable	Required	Description
`POSTHOG_API_KEY`	Yes	Project API key (`phc_…`)
`POSTHOG_HOST`	No	Instance URL — US cloud (default), EU cloud, or self-hosted

Options

const posthog = createPostHogTransport({
  distinctIdField: 'context.accountId',
  eventName: 'api_log'
})

Option	Type	Default	Description
`apiKey`	`string`	`POSTHOG_API_KEY`	Project API key
`host`	`string`	`https://us.i.posthog.com`	PostHog instance URL
`eventName`	`string`	`logixlysia_log`	Name of the captured event
`distinctIdField`	`string`	`context.userId`	Meta path resolved per log to `distinct_id`
`distinctId`	`string`	`logixlysia-server`	Static fallback when the field resolves to nothing

Plus the shared batching options: maxBatchSize, flushIntervalMs, timeout, retries — see the overview.

Payload

Logs post to {host}/batch/. Each event carries flat, chart-friendly properties:

Property	Example
`level`	`INFO`
`message`	`GET /users`
`request.method`	`GET`
`status`	`200`
`durationMs`	`12.4`
`context.requestId`	`0d5e…`

PostHog processes events asynchronously — expect them to appear within about a minute.

Linking Logs to Persons

Merge a user ID into the request context and the log’s distinct_id resolves to it:

app.get('/profile', ({ log, userId }) => {
  log.mergeContext({ userId })
  return getProfile(userId)
})

Point distinctIdField at any other meta path (dot notation) if your identifier lives elsewhere. Without an identifier, events fall back to the static distinctId — handy for a backend acting as a single identity.

Troubleshooting

401 — the key is not a project API key; it must start with phc_.
Events missing — check the region: EU projects must use https://eu.i.posthog.com.
High event volume — log levels you don’t need can be excluded with logFilter before they reach the transport.