Environment Variables

You can use environment variables to configure an existing runtime, to read existing configuration or to build your own runtime based on them.

Environments Passed to Runtimes

Every runtime provides its own unique environment configuration which can be read by a server and the handler.js file during the container run:

Common Environments

Environment	Default	Description
FUNC_HANDLER	main	Deprecated. Use HANDLER_FUNC_NAME instead. Supported only in nodejs20, nodejs22, nodejs24, and python312.
HANDLER_FUNC_NAME	main	The name of the exported Function inside the HANDLER_MOD_NAME file.
MOD_NAME	handler	Deprecated. Use HANDLER_MOD_NAME instead. Supported only in nodejs20, nodejs22, nodejs24, and python312.
HANDLER_MOD_NAME	handler	The name of the main exported file. It must have an extension of .py for the Python runtimes and .js for the Node.js ones. The extension must be added on the server side.
KUBELESS_INSTALL_VOLUME	/kubeless	Deprecated. Use HANDLER_PATH instead. Supported only in nodejs20, nodejs22, nodejs24, and python312.
HANDLER_PATH	/	Full path to volume mount with user's source code.
FUNC_RUNTIME	None	The name of the actual runtime. Possible values: nodejs20 - deprecated, nodejs22, nodejs24, nodejs26, python312, and python314.
TRACE_COLLECTOR_ENDPOINT	None	Full address of OpenTelemetry Trace Collector is exported if the trace collector's endpoint is present.
PUBLISHER_PROXY_ADDRESS	http://eventing-publisher-proxy.kyma-system.svc .cluster.local/publish	Full address of the Publisher Proxy service.

Specific Environments

There are a few environments that occur only for a specific runtimes. The following list includes all of them:

Python Runtime-Specific Environment Variables

Environment	Default	Description
PYTHONPATH	/kubeless/.local:$(PYTHONPATH)	List of directories that Python must add to the sys.path directory list.
PYTHONUNBUFFERED	TRUE	Defines if Python's logs must be buffered before printing them out.

Configure Runtime

You can configure environment variables either separately for a given runtime or make them runtime-agnostic using a ConfigMap.

Define Environment Variables in a Config Map

ConfigMaps allow you to define Function's environment variables for any runtime through key-value pairs. After you define the values in a ConfigMap, simply reference it in the Function custom resource (CR) through the valueFrom parameter. See an example of such a Function CR that specifies the my-var value as a reference to the key stored in the my-vars-cm ConfigMap as the MY_VAR environment variable.

apiVersion: serverless.kyma-project.io/v1alpha2
kind: Function
metadata:
  name: sample-cm-env-values
  namespace: default
spec:
  env:
    - name: MY_VAR
      valueFrom:
        configMapKeyRef:
          key: my-var
          name: my-vars-cm
  runtime: nodejs22
  source:
    inline:
      source: |
        module.exports = {
          main: function (event, context) {
            return process.env["MY_VAR"];
          }
        }

Node.js Runtime-Specific Environment Variables

To configure the Function with the Node.js runtime, override the default values of these environment variables:

Environment variable	Description	Type	Default value
FUNC_TIMEOUT	Specifies the number of seconds in which a runtime must execute the code.	Number	180
REQ_MB_LIMIT	Deprecated. Use FUNC_BODY_MB_LIMIT instead. Supported only in nodejs20, nodejs22, and nodejs24.	Number	1
FUNC_BODY_MB_LIMIT	Specifies the payload body size limit in megabytes.	Number	1
KYMA_INTERNAL_LOGGER_ENABLED	Deprecated. Use SERVER_INTERNAL_LOGGER instead. Supported only in nodejs20, nodejs22, and nodejs24.	Boolean	false
SERVER_INTERNAL_LOGGER	Enables the default HTTP request logger which uses the standard Apache combined log output. To enable it, set its value to true.	Boolean	false

See the example of a Function with these environment variables set:

apiVersion: serverless.kyma-project.io/v1alpha2
kind: Function
metadata:
  name: sample-fn-with-envs
  namespace: default
spec:
  env:
    - name: FUNC_TIMEOUT
      value: '2'
    - name: FUNC_BODY_MB_LIMIT
      value: '10'
  runtime: nodejs26
  source:
    inline:
      source: |
        module.exports = {
          main: function (req, res) {
            res.send("Hello World!");
          }
        }

Python Runtime-Specific Environment Variables

To configure a Function with the Python runtime, override the default values of these environment variables:

Environment variable	Description	Unit	Default value
FUNC_MEMFILE_MAX	Deprecated. Use FUNC_BODY_MB_LIMIT instead. Supported only in python312.	Number	100*1024*1024
FUNC_BODY_MB_LIMIT	Sets the maximum HTTP request body size in megabytes.	Number	1
SERVER_NUMTHREADS	Specifies the number of requests that can be handled in parallel.	Number	50
CHERRYPY_NUMTHREADS	Deprecated. Use SERVER_NUMTHREADS instead. Supported only in python312.	Number	50
KYMA_INTERNAL_LOGGER_ENABLED	Deprecated. Use SERVER_INTERNAL_LOGGER instead. Supported only in python312.	Boolean	false
SERVER_INTERNAL_LOGGER	Enables the default HTTP request logger which uses the standard Apache combined log output. To enable it, set its value to true.	Boolean	false

See kubeless.py to get a deeper understanding of how the Bottle server, which acts as a runtime, uses these values internally to run Python Functions.

apiVersion: serverless.kyma-project.io/v1alpha2
kind: Function
metadata:
  name: sample-fn-with-envs
  namespace: default
spec:
  env:
    - name: FUNC_BODY_MB_LIMIT
      value: '1'
  runtime: python314
  source:
    inline:
      source: |
        def main():
          return "Hello World!"