Merge pull request #29 from srl-labs/env_vars

Add environment variable expansion to topology loader and new utility…

Author: FloSch62

core/data/topology_loader.py

@@ -1,5 +1,8 @@
 import yaml
 import logging
+from core.utils.env_expander import (
+    expand_env_vars,
+)  # if you put the function above in env_expander.py
 
 logger = logging.getLogger(__name__)
 
@@ -10,29 +13,36 @@ class TopologyLoaderError(Exception):
 
 class TopologyLoader:
     """
-    Loads containerlab topology data from a YAML file.
+    Loads containerlab topology data from a YAML file, expanding environment variables.
     """
 
     def load(self, input_file: str) -> dict:
         """
-        Load the containerlab YAML topology file.
+        Load the containerlab YAML topology file, including environment-variable expansion.
 
         :param input_file: Path to the containerlab YAML file.
-        :return: Parsed containerlab topology data.
+        :return: Parsed containerlab topology data with env variables expanded.
         :raises TopologyLoaderError: If file not found or parse error occurs.
         """
         logger.debug(f"Loading topology from file: {input_file}")
         try:
             with open(input_file, "r") as file:
-                containerlab_data = yaml.safe_load(file)
+                raw_content = file.read()
+
+            # Expand ${VAR:=default} placeholders before parsing
+            expanded_content = expand_env_vars(raw_content)
+
+            containerlab_data = yaml.safe_load(expanded_content)
             logger.debug("Topology successfully loaded.")
             return containerlab_data
+
         except FileNotFoundError:
             error_message = (
                 f"Error: The specified clab file '{input_file}' does not exist."
             )
             logger.error(error_message)
             raise TopologyLoaderError(error_message)
+
         except Exception as e:
             error_message = f"An error occurred while loading the config: {e}"
             logger.error(error_message)

core/utils/env_expander.py

@@ -0,0 +1,22 @@
+import os
+import re
+
+
+def expand_env_vars(content: str) -> str:
+    """
+    Expand placeholders of the form ${VAR:=default} or ${VAR:default} in the given string.
+
+    Examples:
+      - ${FOO} will be replaced by os.environ.get("FOO", "")
+      - ${FOO:=bar} will be replaced by os.environ.get("FOO", "bar")
+      - ${FOO:bar} means the same as above (Containerlab also accepts : or :=)
+    """
+    pattern = re.compile(r"\$\{([^:}]+):?=?([^}]*)\}")
+
+    def replacer(match):
+        var_name = match.group(1)
+        default_val = match.group(2)
+        # If the environment variable exists, use it; otherwise, use the default.
+        return os.environ.get(var_name, default_val)
+
+    return pattern.sub(replacer, content)

lab-examples/lab_with_vars.clab.yml

@@ -0,0 +1,19 @@
+name: srl2
+# node names will be srl1 and srl2 unless overridden by CLAB_PREFIX
+prefix: ${CLAB_PREFIX:=""}
+
+topology:
+  nodes:
+    srl1:
+      kind: nokia_srlinux
+      image: ghcr.io/nokia/srlinux:${SRL_VERSION:=latest}
+      type: ${SRL_TYPE:=ixrd3l}
+
+    srl2:
+      kind: nokia_srlinux
+      image: ghcr.io/nokia/srlinux:${SRL_VERSION:=latest}
+      type: ${SRL_TYPE:=ixrd3l}
+
+  links:
+    - endpoints: [srl1:e1-1, srl2:e1-1]
+    - endpoints: [srl1:e1-2, srl2:e1-2]