Debug functions with Data Stream

Send the log messages of your functions, with their level and request ID, to an endpoint with Data Stream, in Azion Console or with the Azion API.

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You can send the log messages of your functions to an endpoint with a Data Stream stream, from Azion Console or with the Azion API. To trace which Rules Engine rules ran on a request instead, refer to Debug rules created with Rules Engine.

A function writes log messages with console.log. The Functions data source carries each message with its level, its source, and the ID of the request, and the Functions Event Collector template places them in one log line per message. For every variable of the data source, refer to Data sources and variables.

Select your interface once. The prerequisites and every task below show only that path.

Prerequisites

  • An Azion account with the Edit Data Stream permission. For the permissions, refer to Stream settings.
  • A function that writes log messages with console.log, running in an application that a workload serves. To create one, refer to Functions.
  • An endpoint that receives the log lines, such as an HTTP endpoint. For the endpoints a stream can send to, refer to Endpoints.

Create the stream

The stream reads the Functions data source of one workload through a workload filter. Unlike sampling, a workload filter leaves your other streams active.

To create the stream with the API, send a POST request to https://api.azion.com/v4/workspace/stream/streams. This example sends the log lines to an HTTP endpoint. Replace <workload-id> with the ID of your workload, and the url and the header with the values of your endpoint:

Shell
01curl -X POST 'https://api.azion.com/v4/workspace/stream/streams' \
02 -H 'Content-Type: application/json' \
03 -H 'Authorization: Token [TOKEN VALUE]' \
04 -d {
05 "name": "functions-debug",
06 "active": true,
07 "inputs": [
08 { "type": "raw_logs", "attributes": { "data_source": "functions_console" } }
09 ],
10 "transform": [
11 { "type": "filter_workloads", "attributes": { "workloads": [<workload-id>] } },
12 { "type": "render_template", "attributes": { "template": 86 } }
13 ],
14 "outputs": [
15 {
16 "type": "standard",
17 "attributes": {
18 "url": "https://logs.example.com/ingest",
19 "headers": { "Authorization": "Bearer [API KEY]" }
20 }
21 }
22 ]
23 }

The functions_console data source is Functions in the Console, and template 86 is Functions Event Collector. A 201 answer carries the stored stream under data. Keep its id: it identifies the stream in every later request, such as /v4/workspace/stream/streams/<stream-id>. For every key of the body, refer to Stream settings.

To create the stream in Azion Console:

Open Data Stream

Access Azion Console > Data Stream.

Select + Stream
Name the stream

In the General section, enter a Name. For example: functions-debug.

Select the Functions data source

In the Input section, select Functions in Data Source.

Turn off Sampling

In the Transform section, turn off Sampling while Option is still All Current and Future Workloads, its starting value. A stream cannot carry sampling and a workload filter together.

Choose the workload

In the Transform section, set Option to Filter Workloads. In Available Workload, select the workload of the function and move it to Chosen Workload with the arrow. For the pick-list controls, refer to Associate workloads with a stream.

Select the template

In the Render Template section, select Functions Event Collector in Template. The Data Set field shows the keys of each log line.

Select the endpoint

In the Output section, select your endpoint in Connector, and enter the fields it shows. Each endpoint has its own fields, listed on Endpoints.

Keep the stream active

In the Status section, keep Active turned on.

Select Save

The Console shows Your data stream has been created. The stream appears in the Data Stream list with functions_console in the Source column and the Active status.

Saving the stream checks the format of each field and does not contact the endpoint. A wrong URL or credential surfaces only when the stream sends. An activation takes effect after one to two minutes.

Confirm the delivery

Real-Time Events records every send of a stream, delivered or not, with the status code the endpoint returned. Send a few requests that run the function, then wait about a minute: a stream sends a batch every 60 seconds, or sooner when it reaches 2,000 log lines.

To read the sends with the API, query the dataStreamedEvents dataset of the Real-Time Events GraphQL API. Replace the dates with a range that covers the activation of the stream:

Shell
01curl -X POST 'https://api.azion.com/v4/events/graphql' \
02 -H 'Content-Type: application/json' \
03 -H 'Authorization: Token [TOKEN VALUE]' \
04 -d '{"query":"query { dataStreamedEvents(limit: 20, filter: {tsRange: {begin: \"2026-10-02T19:25:00\", end: \"2026-10-02T19:45:00\"}}, orderBy: [ts_DESC]) { ts jobName endpointType statusCode streamedLines url } }"}'

The API answers 200 with one record for each send, the latest first:

JSON
01{
02 "data": {
03 "dataStreamedEvents": [
04 {
05 "ts": "2026-10-02T19:29:00Z",
06 …
07 "endpointType": "HTTP_POST",
08 "statusCode": 405,
09 "streamedLines": 2,
10 "url": "https://example.com/logs"
11 },
12 …
13 ]
14 }
15}

statusCode carries the status the endpoint answered, and streamedLines the log lines of the batch. A statusCode of 200 means the endpoint accepted the batch, and an empty dataStreamedEvents list means the stream has not sent in the range. For every field, refer to Real-Time Events GraphQL fields.

To find the sends in Azion Console:

Open Real-Time Events

Access Azion Console > Real-Time Events.

Select the Data Stream data source
Read the latest sends

Each row is one send. Find the rows whose Endpoint Type matches your endpoint, such as HTTP_POST, and read their Status Code.

A Status Code of 200 means the endpoint accepted the batch. Streamed Lines gives the number of log lines in the batch.

A status other than 200 is the answer of the endpoint, and 503 means Data Stream found the endpoint unavailable. For the causes, refer to Troubleshoot Data Stream.

At the endpoint, each log line carries the keys of the Functions Event Collector template. Read these keys to debug the function:

  • logLevel holds the level of the message: ERROR, WARN, INFO, DEBUG, or TRACE. It carries the $log_level variable.
  • logMessage holds the message the function passed to the log function. It carries the $log_message variable.
  • messageSource reads CONSOLE for a message written with the console API, such as console.log, and RUNTIME for an error message.
  • requestID identifies the request, so the messages of one request share it.

To keep the variable names as keys, or to send fewer of them, select a custom template instead. For an example data set, refer to Templates and payload.

Next steps

Data sources and variablesRead what each variable of the Functions data source holds, with an example value.FunctionsWrite and run the functions whose messages the stream collects.Create a custom templateChoose which Functions variables each log line carries, and under which keys.Troubleshoot Data StreamFind what to change when a send returns a status other than 200.