docker: inject config files into containers via extra_configs

Add an `extra_configs` field (list of {target, content}) to the docker
node/template/appliance schemas. For each entry GNS3 writes `content` to a
file in the node working directory and bind-mounts it read-only at `target`
inside the container.

This lets a NOS appliance seed its startup config without rebuilding the
image: XRd points XR_FIRST_BOOT_CONFIG at an injected /firstboot.cfg, FRR at
/etc/frr/frr.conf, etc. The bind is a single-file mount applied at create
time, so it works for both the generic init.sh path and vendor nodes that
skip init.sh (console_type=docker_exec). Entries are only injected when
present, so ordinary nodes are unaffected.

The content can't go through `environment` (it is line-delimited, one var per
line), hence a dedicated field -- the same plumbing shape as extra_volumes.

gns3server/api/routes/compute/docker_nodes.py

@@ -78,6 +78,7 @@ async def create_docker_node(project_id: UUID, node_data: schemas.DockerCreate)
         aux_type=node_data.pop("aux_type", "none"),
         extra_hosts=node_data.get("extra_hosts"),
         extra_volumes=node_data.get("extra_volumes"),
+        extra_configs=node_data.get("extra_configs"),
         memory=node_data.get("memory", 0),
         cpus=node_data.get("cpus", 0),
     )
@@ -87,7 +88,8 @@ async def create_docker_node(project_id: UUID, node_data: schemas.DockerCreate)
     for key in (
         "console", "console_type", "console_resolution", "console_http_port",
         "console_http_path", "aux", "aux_type", "start_command", "environment",
-        "adapters", "mac_address", "extra_hosts", "extra_volumes", "memory", "cpus",
+        "adapters", "mac_address", "extra_hosts", "extra_volumes", "extra_configs",
+        "memory", "cpus",
     ):
         node_data.pop(key, None)
     for name, value in node_data.items():
@@ -137,6 +139,7 @@ async def update_docker_node(node_data: schemas.DockerUpdate, node: DockerVM = D
         "custom_adapters",
         "extra_hosts",
         "extra_volumes",
+        "extra_configs",
         "memory",
         "cpus",
     ]

gns3server/compute/docker/docker_vm.py

@@ -89,6 +89,7 @@ class DockerVM(BaseNode):
         console_http_path="/",
         extra_hosts=None,
         extra_volumes=[],
+        extra_configs=None,
         memory=0,
         cpus=0,
     ):
@@ -118,6 +119,7 @@ class DockerVM(BaseNode):
         self._console_websocket = None
         self._extra_hosts = extra_hosts
         self._extra_volumes = extra_volumes or []
+        self._extra_configs = extra_configs or []
         self._memory = memory
         self._cpus = cpus
         self._permissions_fixed = True
@@ -164,6 +166,7 @@ class DockerVM(BaseNode):
             "node_directory": self.working_path,
             "extra_hosts": self.extra_hosts,
             "extra_volumes": self.extra_volumes,
+            "extra_configs": self.extra_configs,
             "memory": self.memory,
             "cpus": self.cpus,
         }
@@ -295,6 +298,14 @@ class DockerVM(BaseNode):
     def extra_volumes(self, extra_volumes):
         self._extra_volumes = extra_volumes
 
+    @property
+    def extra_configs(self):
+        return self._extra_configs
+
+    @extra_configs.setter
+    def extra_configs(self, extra_configs):
+        self._extra_configs = extra_configs or []
+
     @property
     def memory(self):
         return self._memory
@@ -391,6 +402,28 @@ class DockerVM(BaseNode):
                 "Target": "/gns3volumes{}".format(volume)
             })
 
+        # Inject extra config files: write each to the node working directory and
+        # bind-mount it read-only at its target path. Single-file binds are applied
+        # at create time, so this works for the generic init.sh path AND for vendor
+        # nodes that skip init.sh (the NOS reads its startup config from the mount).
+        for cfg in self._extra_configs:
+            target = cfg["target"] if isinstance(cfg, dict) else cfg.target
+            content = cfg["content"] if isinstance(cfg, dict) else cfg.content
+            if not target.startswith("/") or ".." in target.split("/"):
+                raise DockerError(
+                    f"Extra config target '{target}' must be an absolute path and not contain '..'."
+                )
+            host_path = os.path.join(self.working_dir, "configs", target.lstrip("/"))
+            os.makedirs(os.path.dirname(host_path), exist_ok=True)
+            with open(host_path, "w") as f:
+                f.write(content)
+            binds.append({
+                "Type": "bind",
+                "Source": host_path,
+                "Target": target,
+                "ReadOnly": True,
+            })
+
         return binds
 
     def _create_network_config(self):

gns3server/schemas/common.py

@@ -48,6 +48,19 @@ class CustomAdapter(BaseModel):
     mac_address: Optional[str] = Field(None, pattern="^([0-9a-fA-F]{2}[:]){5}([0-9a-fA-F]{2})$")
 
 
+class ExtraConfig(BaseModel):
+    """
+    A configuration file injected into a Docker container.
+
+    GNS3 writes ``content`` to a host file and bind-mounts it read-only at
+    ``target`` inside the container. Used to seed NOS startup configs (e.g.
+    XRd first-boot config, FRR frr.conf) without rebuilding the image.
+    """
+
+    target: str = Field(..., description="Absolute path inside the container where the file is mounted")
+    content: str = Field("", description="File content written by GNS3 and bind-mounted read-only into the container")
+
+
 class ConsoleType(str, Enum):
     """
     Supported console types.

gns3server/schemas/compute/docker_nodes.py

@@ -18,7 +18,7 @@ from pydantic import BaseModel, Field
 from typing import Optional, List
 from uuid import UUID
 
-from ..common import NodeStatus, CustomAdapter, ConsoleType, AuxType
+from ..common import NodeStatus, CustomAdapter, ConsoleType, AuxType, ExtraConfig
 
 
 class DockerBase(BaseModel):
@@ -43,6 +43,7 @@ class DockerBase(BaseModel):
     environment: Optional[str] = Field(None, description="Docker environment variables")
     extra_hosts: Optional[str] = Field(None, description="Docker extra hosts (added to /etc/hosts)")
     extra_volumes: Optional[List[str]] = Field(None, description="Additional directories to make persistent")
+    extra_configs: Optional[List[ExtraConfig]] = Field(None, description="Configuration files injected into the container (bind-mounted read-only)")
     memory: Optional[int] = Field(None, ge=0, description="Maximum amount of memory the container can use in MB")
     cpus: Optional[float] = Field(None, ge=0, description="Maximum amount of CPU resources the container can use")
     custom_adapters: Optional[List[CustomAdapter]] = Field(None, description="Custom adapters")

gns3server/schemas/controller/appliances.py

@@ -20,6 +20,7 @@ from enum import Enum
 from typing import Annotated, List, Literal, Optional, Union
 from uuid import UUID
 from pydantic import AnyUrl, BaseModel, Discriminator, EmailStr, Field, Tag
+from ..common import ExtraConfig
 
 
 # ============================================================================
@@ -329,6 +330,7 @@ class Docker(BaseModel):
     console_http_path: Optional[str] = Field(None, description='Path of the web interface')
     extra_hosts: Optional[str] = Field(None, description='Hosts which will be written to /etc/hosts into container')
     extra_volumes: Optional[List[str]] = Field(None, description='Additional directories to make persistent that are not included in the images VOLUME directive')
+    extra_configs: Optional[List[ExtraConfig]] = Field(None, description='Configuration files injected into the container (bind-mounted read-only)')
 
 
 class Iou(BaseModel):
@@ -479,6 +481,9 @@ class DockerPropertiesV8(BaseModel):
     extra_volumes: Optional[List[str]] = Field(
         None, title='Additional directories to make persistent'
     )
+    extra_configs: Optional[List[ExtraConfig]] = Field(
+        None, title='Configuration files injected into the container (bind-mounted read-only)'
+    )
 
 
 class IouPropertiesV8(BaseModel):

gns3server/schemas/controller/templates/docker_templates.py

@@ -16,7 +16,7 @@
 
 
 from . import Category, TemplateBase
-from ...common import ConsoleType, AuxType, CustomAdapter
+from ...common import ConsoleType, AuxType, CustomAdapter, ExtraConfig
 
 from pydantic import Field
 from typing import Optional, List
@@ -49,6 +49,7 @@ class DockerTemplate(TemplateBase):
     )
     extra_hosts: Optional[str] = Field("", description="Docker extra hosts (added to /etc/hosts)")
     extra_volumes: Optional[List] = Field([], description="Additional directories to make persistent")
+    extra_configs: Optional[List[ExtraConfig]] = Field(default_factory=list, description="Configuration files injected into the container (bind-mounted read-only)")
     memory: Optional[int] = Field(0, ge=0, description="Maximum amount of memory the container can use in MB")
     cpus: Optional[float] = Field(0, ge=0, description="Maximum amount of CPU resources the container can use")
     custom_adapters: Optional[List[CustomAdapter]] = Field(default_factory=list, description="Custom adapters")

tests/compute/docker/test_docker_vm.py

@@ -69,6 +69,7 @@ def test_json(vm, compute_project):
         'console_http_path': '/',
         'extra_hosts': None,
         'extra_volumes': [],
+        'extra_configs': [],
         'memory': 0,
         'cpus': 0,
         'aux': vm.aux,
@@ -307,6 +308,44 @@ async def test_create_applies_env_host_config(compute_project, manager):
             ), "GNS3_ user vars must not leak into the container environment"
 
 
+@pytest.mark.asyncio
+async def test_create_with_extra_configs(compute_project, manager):
+    """
+    extra_configs entries are written to the node working directory and
+    bind-mounted read-only at their target path inside the container.
+    """
+
+    extra_configs = [{"target": "/firstboot.cfg", "content": "username clab\n!\nend"}]
+    response = {"Id": "e90e34656806", "Warnings": []}
+
+    with asyncio_patch("gns3server.compute.docker.Docker.list_images", return_value=[{"image": "ubuntu"}]):
+        with asyncio_patch("gns3server.compute.docker.Docker.query", return_value=response) as mock:
+            vm = DockerVM("test", str(uuid.uuid4()), compute_project, manager, "ubuntu", extra_configs=extra_configs)
+            await vm.create()
+            mounts = mock.call_args[1]["data"]["HostConfig"]["Mounts"]
+            injected = [m for m in mounts if m.get("Target") == "/firstboot.cfg"]
+            assert len(injected) == 1
+            assert injected[0]["ReadOnly"] is True
+            with open(injected[0]["Source"]) as f:
+                assert f.read() == "username clab\n!\nend"
+
+
+@pytest.mark.asyncio
+async def test_create_with_extra_configs_invalid_target(compute_project, manager):
+    """
+    An extra_configs target that is not absolute (or contains '..') is rejected.
+    """
+
+    extra_configs = [{"target": "relative/path", "content": "x"}]
+    response = {"Id": "e90e34656806", "Warnings": []}
+
+    with asyncio_patch("gns3server.compute.docker.Docker.list_images", return_value=[{"image": "ubuntu"}]):
+        with asyncio_patch("gns3server.compute.docker.Docker.query", return_value=response):
+            vm = DockerVM("test", str(uuid.uuid4()), compute_project, manager, "ubuntu", extra_configs=extra_configs)
+            with pytest.raises(DockerError):
+                await vm.create()
+
+
 @pytest.mark.asyncio
 async def test_create_with_colon_in_project_name(compute_project, manager):