fix: Use CONDA_DEFAULT_ENV presence as a flag to use conda mode (#1555)

# What does this PR do?

This is the second attempt to switch to system packages by default. Now
with a hack to detect conda environment - in which case conda image-type
is used.

Note: Conda will only be used when --image-name is unset *and*
CONDA_DEFAULT_ENV is set. This means that users without conda will
correctly fall back to using system packages when no --image-* arguments
are passed at all.

[//]: # (If resolving an issue, uncomment and update the line below)
[//]: # (Closes #[issue-number])

## Test Plan

Uses virtualenv:

```
$ llama stack build --template ollama --image-type venv
$ llama stack run --image-type venv ~/.llama/distributions/ollama/ollama-run.yaml
[...]
Using virtual environment: /home/ec2-user/src/llama-stack/schedule/.local
[...]
```

Uses system packages (virtualenv already initialized):

```
$ llama stack run ~/.llama/distributions/ollama/ollama-run.yaml
[...]
INFO     2025-03-27 20:46:22,882 llama_stack.cli.stack.run:142 server: No image type or image name provided. Assuming environment packages.
[...]
```

Attempt to run from environment packages without necessary packages
installed:
```
$ python -m venv barebones
$ . ./barebones/bin/activate
$ pip install -e . # to install llama command
$ llama stack run ~/.llama/distributions/ollama/ollama-run.yaml
[...]
ModuleNotFoundError: No module named 'fastapi'
```

^ failed as expected because the environment doesn't have necessary
packages installed.

Now install some packages in the new environment:

```
$ pip install fastapi opentelemetry-api opentelemetry-sdk opentelemetry-exporter-otlp aiosqlite ollama openai datasets faiss-cpu mcp autoevals
$ llama stack run ~/.llama/distributions/ollama/ollama-run.yaml
[...]
Uvicorn running on http://['::', '0.0.0.0']:8321 (Press CTRL+C to quit)
```

Now see if setting CONDA_DEFAULT_ENV will change what happens by
default:

```
$ export CONDA_DEFAULT_ENV=base
$ llama stack run ~/.llama/distributions/ollama/ollama-run.yaml
[...]
Using conda environment: base
Conda environment base does not exist.
[...]
```

---------

Signed-off-by: Ihar Hrachyshka <ihar.hrachyshka@gmail.com>

llama_stack/cli/stack/_build.py

@@ -21,6 +21,7 @@ from prompt_toolkit.completion import WordCompleter
 from prompt_toolkit.validation import Validator
 from termcolor import cprint
 
+from llama_stack.cli.stack.utils import ImageType
 from llama_stack.cli.table import print_table
 from llama_stack.distribution.build import (
     SERVER_DEPENDENCIES,
@@ -62,10 +63,10 @@ def run_stack_build_command(args: argparse.Namespace) -> None:
     if args.list_templates:
         return _run_template_list_cmd()
 
-    if args.image_type == "venv":
+    if args.image_type == ImageType.VENV.value:
         current_venv = os.environ.get("VIRTUAL_ENV")
         image_name = args.image_name or current_venv
-    elif args.image_type == "conda":
+    elif args.image_type == ImageType.CONDA.value:
         current_conda_env = os.environ.get("CONDA_DEFAULT_ENV")
         image_name = args.image_name or current_conda_env
     else:
@@ -84,7 +85,7 @@ def run_stack_build_command(args: argparse.Namespace) -> None:
             build_config.image_type = args.image_type
         else:
             cprint(
-                f"Please specify a image-type (container | conda | venv) for {args.template}",
+                f"Please specify a image-type ({' | '.join(e.value for e in ImageType)}) for {args.template}",
                 color="red",
             )
             sys.exit(1)
@@ -98,15 +99,15 @@ def run_stack_build_command(args: argparse.Namespace) -> None:
         )
 
         image_type = prompt(
-            "> Enter the image type you want your Llama Stack to be built as (container or conda or venv): ",
+            f"> Enter the image type you want your Llama Stack to be built as ({' or '.join(e.value for e in ImageType)}): ",
             validator=Validator.from_callable(
-                lambda x: x in ["container", "conda", "venv"],
-                error_message="Invalid image type, please enter conda or container or venv",
+                lambda x: x in [e.value for e in ImageType],
+                error_message=f"Invalid image type, please enter {' or '.join(e.value for e in ImageType)}",
             ),
-            default="conda",
+            default=ImageType.CONDA.value,
         )
 
-        if image_type == "conda":
+        if image_type == ImageType.CONDA.value:
             if not image_name:
                 cprint(
                     f"No current conda environment detected or specified, will create a new conda environment with the name `llamastack-{name}`",

llama_stack/cli/stack/build.py

@@ -6,6 +6,7 @@
 import argparse
 import textwrap
 
+from llama_stack.cli.stack.utils import ImageType
 from llama_stack.cli.subcommand import Subcommand
 
 
@@ -46,16 +47,16 @@ class StackBuild(Subcommand):
         self.parser.add_argument(
             "--image-type",
             type=str,
-            help="Image Type to use for the build. This can be either conda or container or venv. If not specified, will use the image type from the template config.",
-            choices=["conda", "container", "venv"],
-            default="conda",
+            help="Image Type to use for the build. If not specified, will use the image type from the template config.",
+            choices=[e.value for e in ImageType],
+            default=ImageType.CONDA.value,
         )
 
         self.parser.add_argument(
             "--image-name",
             type=str,
             help=textwrap.dedent(
-                """[for image-type=conda|venv] Name of the conda or virtual environment to use for
+                f"""[for image-type={"|".join(e.value for e in ImageType)}] Name of the conda or virtual environment to use for
 the build. If not specified, currently active Conda environment will be used if found.
             """
             ),

llama_stack/cli/stack/run.py

@@ -8,6 +8,7 @@ import argparse
 import os
 from pathlib import Path
 
+from llama_stack.cli.stack.utils import ImageType
 from llama_stack.cli.subcommand import Subcommand
 from llama_stack.log import get_logger
 
@@ -43,7 +44,7 @@ class StackRun(Subcommand):
         self.parser.add_argument(
             "--image-name",
             type=str,
-            default=None,
+            default=os.environ.get("CONDA_DEFAULT_ENV"),
             help="Name of the image to run. Defaults to the current conda environment",
         )
         self.parser.add_argument(
@@ -56,7 +57,6 @@ class StackRun(Subcommand):
             "--env",
             action="append",
             help="Environment variables to pass to the server in KEY=VALUE format. Can be specified multiple times.",
-            default=[],
             metavar="KEY=VALUE",
         )
         self.parser.add_argument(
@@ -73,10 +73,24 @@ class StackRun(Subcommand):
             "--image-type",
             type=str,
             help="Image Type used during the build. This can be either conda or container or venv.",
-            choices=["conda", "container", "venv"],
-            default="conda",
+            choices=[e.value for e in ImageType],
         )
 
+    # If neither image type nor image name is provided, but at the same time
+    # the current environment has conda breadcrumbs, then assume what the user
+    # wants to use conda mode and not the usual default mode (using
+    # pre-installed system packages).
+    #
+    # Note: yes, this is hacky. It's implemented this way to keep the existing
+    # conda users unaffected by the switch of the default behavior to using
+    # system packages.
+    def _get_image_type_and_name(self, args: argparse.Namespace) -> tuple[str, str]:
+        conda_env = os.environ.get("CONDA_DEFAULT_ENV")
+        if conda_env and args.image_name == conda_env:
+            logger.warning(f"Conda detected. Using conda environment {conda_env} for the run.")
+            return ImageType.CONDA.value, args.image_name
+        return args.image_type, args.image_name
+
     def _run_stack_run_cmd(self, args: argparse.Namespace) -> None:
         import yaml
 
@@ -120,20 +134,44 @@ class StackRun(Subcommand):
         except AttributeError as e:
             self.parser.error(f"failed to parse config file '{config_file}':\n {e}")
 
-        run_args = formulate_run_args(args.image_type, args.image_name, config, template_name)
+        image_type, image_name = self._get_image_type_and_name(args)
 
-        run_args.extend([str(config_file), str(args.port)])
-        if args.disable_ipv6:
-            run_args.append("--disable-ipv6")
+        # If neither image type nor image name is provided, assume the server should be run directly
+        # using the current environment packages.
+        if not image_type and not image_name:
+            logger.info("No image type or image name provided. Assuming environment packages.")
+            from llama_stack.distribution.server.server import main as server_main
 
-        for env_var in args.env:
-            if "=" not in env_var:
-                self.parser.error(f"Environment variable '{env_var}' must be in KEY=VALUE format")
-            key, value = env_var.split("=", 1)  # split on first = only
-            if not key:
-                self.parser.error(f"Environment variable '{env_var}' has empty key")
-            run_args.extend(["--env", f"{key}={value}"])
+            # Build the server args from the current args passed to the CLI
+            server_args = argparse.Namespace()
+            for arg in vars(args):
+                # If this is a function, avoid passing it
+                # "args" contains:
+                # func=<bound method StackRun._run_stack_run_cmd of <llama_stack.cli.stack.run.StackRun object at 0x10484b010>>
+                if callable(getattr(args, arg)):
+                    continue
+                setattr(server_args, arg, getattr(args, arg))
 
-        if args.tls_keyfile and args.tls_certfile:
-            run_args.extend(["--tls-keyfile", args.tls_keyfile, "--tls-certfile", args.tls_certfile])
-        run_command(run_args)
+            # Run the server
+            server_main(server_args)
+        else:
+            run_args = formulate_run_args(image_type, image_name, config, template_name)
+
+            run_args.extend([str(config_file), str(args.port)])
+            if args.disable_ipv6:
+                run_args.append("--disable-ipv6")
+
+            if args.env:
+                for env_var in args.env:
+                    if "=" not in env_var:
+                        self.parser.error(f"Environment variable '{env_var}' must be in KEY=VALUE format")
+                        return
+                    key, value = env_var.split("=", 1)  # split on first = only
+                    if not key:
+                        self.parser.error(f"Environment variable '{env_var}' has empty key")
+                        return
+                    run_args.extend(["--env", f"{key}={value}"])
+
+            if args.tls_keyfile and args.tls_certfile:
+                run_args.extend(["--tls-keyfile", args.tls_keyfile, "--tls-certfile", args.tls_certfile])
+            run_command(run_args)

llama_stack/cli/stack/utils.py

@@ -4,6 +4,14 @@
 # This source code is licensed under the terms described in the LICENSE file in
 # the root directory of this source tree.
 
+from enum import Enum
+
+
+class ImageType(Enum):
+    CONDA = "conda"
+    CONTAINER = "container"
+    VENV = "venv"
+
 
 def print_subcommand_description(parser, subparsers):
     """Print descriptions of subcommands."""