Allow images to be built on the fly.

src/constellation/__init__.py

@@ -5,9 +5,10 @@
     ConstellationService,
     ConstellationVolumeMount,
 )
-from constellation.util import ImageReference
+from constellation.util import BuildSpec, ImageReference
 
 __all__ = [
+    "BuildSpec",
     "Constellation",
     "ConstellationBindMount",
     "ConstellationContainer",

src/constellation/constellation.py

@@ -1,11 +1,11 @@
 from abc import abstractmethod
 from pathlib import Path
-from typing import Optional
+from typing import Optional, Union
 
 import docker
 
 from constellation import docker_util, vault
-from constellation.util import rand_str, tabulate
+from constellation.util import BuildSpec, ImageReference, rand_str, tabulate
 
 
 class Constellation:
@@ -65,8 +65,7 @@ def start(self, pull_images=False, subset=None):
             raise Exception(msg)
         if self.vault_config:
             vault.resolve_secrets(self.data, self.vault_config.client())
-        if pull_images:
-            self.containers.pull_images()
+        self.containers.prepare_images(pull=pull_images)
         self.network.create()
         self.volumes.create()
         self.containers.start(
@@ -82,8 +81,7 @@ def stop(self, kill=False, remove_network=False, remove_volumes=False):
             self.volumes.remove()
 
     def restart(self, pull_images=True):
-        if pull_images:
-            self.containers.pull_images()
+        self.containers.prepare_images(pull=pull_images)
         self.stop()
         self.start()
 
@@ -118,7 +116,7 @@ class ConstellationContainer:
     def __init__(
         self,
         name,
-        image,
+        image: Union[ImageReference, BuildSpec],
         args=None,
         mounts=None,
         ports=None,
@@ -143,20 +141,28 @@ def __init__(
         self.labels = labels
         self.preconfigure = preconfigure
         self.network = network
+        self.image_id = None
 
     def name_external(self, prefix):
         return f"{prefix}-{self.name}"
 
-    def pull_image(self):
-        docker_util.image_pull(self.name, str(self.image))
+    def prepare_image(self, *, pull: bool):
+        if isinstance(self.image, BuildSpec):
+            self.image_id = docker_util.image_build(self.name, self.image)
+        elif pull:
+            docker_util.image_pull(self.name, str(self.image))
+            self.image_id = str(self.image)
+        else:
+            docker_util.ensure_image(self.name, str(self.image))
+            self.image_id = str(self.image)
 
     def exists(self, prefix):
         return docker_util.container_exists(self.name_external(prefix))
 
     def start(self, prefix, network, volumes, data=None):
         cl = docker.client.from_env()
         nm = self.name_external(prefix)
-        print(f"Starting {self.name} ({self.image!s})")
+        print(f"Starting {self.name} ({self.image_id})")
         mounts = [x.to_mount(volumes) for x in self.mounts]
 
         if self.ports_config:
@@ -171,9 +177,8 @@ def start(self, prefix, network, volumes, data=None):
         networking_config = cl.api.create_networking_config(
             {f"{network.name}": endpoint_config}
         )
-        docker_util.ensure_image(self.name, str(self.image))
         x_obj = cl.api.create_container(
-            str(self.image),
+            self.image_id,
             self.args,
             name=nm,
             detach=True,
@@ -221,7 +226,9 @@ def remove(self, prefix):
 # This could be achieved by inheriting from ConstellationContainer but
 # this seems more like a has-a than an is-a relationship.
 class ConstellationService:
-    def __init__(self, name, image, scale, **kwargs):
+    def __init__(
+        self, name, image: Union[ImageReference, BuildSpec], scale, **kwargs
+    ):
         self.name = name
         self.image = image
         self.scale = scale
@@ -231,8 +238,8 @@ def __init__(self, name, image, scale, **kwargs):
     def name_external(self, prefix):
         return f"{self.base.name_external(prefix)}-<i>"
 
-    def pull_image(self):
-        self.base.pull_image()
+    def prepare_image(self, *, pull: bool):
+        return self.base.prepare_image(pull=pull)
 
     def exists(self, prefix):
         return bool(self.get(prefix))
@@ -242,6 +249,7 @@ def start(self, prefix, network, volumes, data=None):
         for _i in range(self.scale):
             name = f"{self.name}-{rand_str(8)}"
             container = ConstellationContainer(name, self.image, **self.kwargs)
+            container.image_id = self.base.image_id
             container.start(prefix, network, volumes, data)
 
     def get(self, prefix, stopped=False):
@@ -285,13 +293,13 @@ def get(self, name, prefix):
     def exists(self, prefix):
         return [x.exists(prefix) for x in self.collection]
 
-    def _apply(self, method, *args, subset=None):
+    def _apply(self, method, *args, subset=None, **kwargs):
         for x in self.collection:
             if subset is None or x.name in subset:
-                x.__getattribute__(method)(*args)
+                x.__getattribute__(method)(*args, **kwargs)
 
-    def pull_images(self):
-        self._apply("pull_image")
+    def prepare_images(self, *, pull):
+        self._apply("prepare_image", pull=pull)
 
     def stop(self, prefix, kill=False):
         self._apply("stop", prefix, kill)

src/constellation/docker_util.py

@@ -6,6 +6,8 @@
 
 import docker
 
+from constellation.util import BuildSpec
+
 
 def ensure_network(name):
     client = docker.client.from_env()
@@ -227,6 +229,14 @@ def image_pull(name, ref):
     return prev != curr
 
 
+def image_build(name: str, spec: BuildSpec):
+    client = docker.client.from_env()
+    print(f"Building docker image for {name} from {spec.path}")
+    image, _ = client.images.build(path=spec.path)
+    print(f"    `-> {image.id}")
+    return image.id
+
+
 def containers_matching(prefix, stopped):
     cl = docker.client.from_env()
     return [x for x in cl.containers.list(stopped) if x.name.startswith(prefix)]

src/constellation/util.py

@@ -1,17 +1,24 @@
 import random
 import string
+from dataclasses import dataclass
 
 
+@dataclass
 class ImageReference:
-    def __init__(self, repo, name, tag):
-        self.repo = repo
-        self.name = name
-        self.tag = tag
+    repo: str
+    name: str
+    tag: str
 
     def __str__(self):
         return f"{self.repo}/{self.name}:{self.tag}"
 
 
+@dataclass
+class BuildSpec:
+    # Path to the directory containing the Dockerfile
+    path: str
+
+
 def tabulate(x):
     ret = {}
     for el in x:

tests/test_constellation.py

@@ -20,7 +20,7 @@
     port_config,
     vault,
 )
-from constellation.util import ImageReference, rand_str
+from constellation.util import BuildSpec, ImageReference, rand_str
 
 
 def drop_image(ref):
@@ -200,33 +200,25 @@ def test_container_simple():
     assert f.getvalue() == ""
 
 
-def test_pull_missing_container_on_start(capsys):
+def test_pull_missing_container_on_prepare(capsys):
     nm = rand_str(n=10, prefix="")
     ref = ImageReference("library", "redis", "5.0")
 
     drop_image(str(ref))
 
     x = ConstellationContainer(nm, ref)
-    assert x.name_external("prefix") == f"prefix-{nm}"
-    assert not x.exists("prefix")
-    assert x.get("prefix") is None
-    nw = ConstellationNetwork(constellation_rand_str())
-    nw.create()
+    x.prepare_image(pull=False)
 
-    x.start("prefix", network=nw, volumes=None)
     res = capsys.readouterr()
     assert "Pulling docker image" in res.out
-    x.stop("prefix")
-    x.stop("prefix", True)
-    x.remove("prefix")
-    nw.remove()
 
 
 def test_container_start_stop_remove():
     nm = rand_str(n=10, prefix="")
     cl = docker.client.from_env()
     cl.images.pull("library/redis:5.0")
     x = ConstellationContainer(nm, "library/redis:5.0")
+    x.prepare_image(pull=False)
     nw = ConstellationNetwork(constellation_rand_str())
     try:
         nw.create()
@@ -250,6 +242,7 @@ def configure(container, _data):
         cl = docker.client.from_env()
         cl.images.pull("library/redis:5.0")
         x = ConstellationContainer(nm, "library/redis:5.0", configure=configure)
+        x.prepare_image(pull=False)
         nw = ConstellationNetwork(constellation_rand_str())
         nw.create()
         x.start("prefix", nw, None)
@@ -268,6 +261,7 @@ def test_container_ports():
         x = ConstellationContainer(
             nm, "library/alpine:latest", ports=[80, (3000, 8080)]
         )
+        x.prepare_image(pull=False)
         nw = ConstellationNetwork(constellation_rand_str())
         nw.create()
         x.start("prefix", nw, None)
@@ -286,7 +280,7 @@ def test_container_pull():
     ref = "library/hello-world:latest"
     x = ConstellationContainer("hello", ref)
     drop_image(ref)
-    x.pull_image()
+    x.prepare_image(pull=True)
     assert docker_util.image_exists(ref)
 
 
@@ -306,7 +300,7 @@ def test_container_collection():
         obj.get("foo", prefix)
 
     assert obj.exists(prefix) == [False, False]
-    obj.pull_images()
+    obj.prepare_images(pull=True)
     obj.start(prefix, nw, [])
 
     cl = obj.get("client", prefix)
@@ -636,3 +630,22 @@ def test_constellation_can_set_labels():
     assert container_label.get("prefix").labels == labels
 
     obj.destroy()
+
+
+def test_constellation_can_build_image(tmp_path):
+    (tmp_path / "Dockerfile").write_text(
+        """
+FROM alpine:latest
+CMD ["echo", "Hello, World"]
+"""
+    )
+
+    container = ConstellationContainer("container", BuildSpec(str(tmp_path)))
+
+    obj = Constellation("project", "prefix", [container], "network", None)
+    obj.start()
+
+    log = container.get("prefix").logs().decode("utf-8")
+    assert "Hello, World\n" == log
+
+    obj.destroy()