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|
"""Turn a `container.toml` into a `modal.Image` and a `modal.App`.
Every container -- under `containers/` here, `.modal/` in a repo that merely
builds itself on Modal -- is a directory with a `container.toml` and
a stub `container.py`. See `spec.md` for the keys; this file is what reads
them. Nothing here is Modal-specific configuration in its own right -- each
spec key maps onto a documented Modal argument, and the mapping is meant to
stay boring enough to read straight through.
"""
import os
import shlex
import subprocess
import tomllib
import modal
REPO = os.path.dirname(os.path.dirname(os.path.abspath(__file__)))
PTYSHIM_C = os.path.join(REPO, "ptyshim.c")
SHIM_SO = "/opt/ptyshim.so"
class SpecError(Exception):
"""The container.toml says something that cannot be built."""
def _running_in_modal() -> bool:
"""True inside a Modal container, false on the machine that launched it."""
return bool(os.environ.get("MODAL_TASK_ID"))
class Container:
"""One container: its spec, its image, its app, and how to run it."""
def __init__(self, spec: dict, directory: str):
self.is_remote = _running_in_modal()
self.dir = directory
self.spec = spec
self.name = self._require("container", "name")
self.description = spec.get("container", {}).get("description", "")
run = spec.get("run", {})
self.workdir = run.get("workdir", "/app")
self.command = run.get("command", "")
self.env = dict(run.get("env", {}))
# Substituters reach nix through NIX_CONFIG rather than nix.conf, and
# at run time rather than build time. Written into the image's nix.conf
# instead, nix touches the path while the image is being built and
# creates it -- and Modal will not mount a volume over a non-empty
# directory, so the container that wanted the cache cannot start. As
# env it covers every nix command that runs in the container, the ones
# typed by hand in a shell included, and leaves the mount point empty.
if subs := list(spec.get("nix", {}).get("substituters", [])):
line = "extra-substituters = " + " ".join(subs)
self.env["NIX_CONFIG"] = (
f"{self.env['NIX_CONFIG']}\n{line}" if "NIX_CONFIG" in self.env
else line
)
# "function" (the default) or "sandbox". Sandboxes can run on a real
# VM, which Functions cannot -- see ../README.md.
self.runtime = spec.get("container", {}).get("runtime", "function")
nix = spec.get("nix", {})
self.use_flake = bool(nix.get("flake", False))
self.use_shim = bool(nix.get("shim", False))
# name -> mount path. Modal Volumes, mounted while the container runs
# and NOT while its image is built: a volume mount is not part of the
# resulting image, so anything written to one during a build step is
# gone by the time the container starts. Persist across runs is the
# whole point -- a nix store to substitute from, a cargo target
# directory, a dataset too big to bake in.
self.volume_spec = dict(spec.get("volumes", {}))
# Ports to tunnel out of a Sandbox, from [network] ports. Encrypted,
# which is Modal's own word for "the tunnel terminates TLS and speaks
# plain HTTP to your process" -- so the thing listening inside is an
# ordinary http.server and not something holding a certificate.
#
# Sandbox-only: a Function has no long-lived process to tunnel into,
# and `modal run` on one would hand back a URL for a container that
# has already exited.
self.ports = [int(p) for p in spec.get("network", {}).get("ports", [])]
# Modal re-imports this module inside the container, so everything
# below runs twice: once here, once out there. Out there the local
# tree does not exist -- no flake.nix, no ptyshim.c, no repo -- and
# the image is already built, so validating and rebuilding it would
# only fail. The App still has to exist for the decorators to bind.
if self.is_remote:
self.image = None
self.app = modal.App(self.name)
else:
self._validate()
self.image = self._build_image()
self.app = modal.App(self.name, image=self.image)
# -- spec reading ----------------------------------------------------
@classmethod
def from_toml(cls, container_py: str) -> "Container":
"""Load the container.toml sitting next to the given container.py."""
directory = os.path.dirname(os.path.abspath(container_py))
path = os.path.join(directory, "container.toml")
if not os.path.exists(path):
raise SpecError(f"no container.toml in {directory}")
with open(path, "rb") as f:
return cls(tomllib.load(f), directory)
def _require(self, table: str, key: str):
try:
return self.spec[table][key]
except KeyError:
raise SpecError(f"container.toml needs [{table}] {key}") from None
def _validate(self):
c = self.spec.get("container", {})
if self.runtime not in ("function", "sandbox"):
raise SpecError(
f'[container] runtime must be "function" or "sandbox",'
f" not {self.runtime!r}"
)
if bool(c.get("base")) == bool(c.get("registry")):
raise SpecError("set exactly one of [container] base or registry")
if self.use_flake:
if not os.path.exists(os.path.join(self.dir, "flake.nix")):
raise SpecError("[nix] flake = true but there is no flake.nix")
if not self.use_shim:
# Warming the shell builds nix-shell-env, which is the gVisor
# pty bug. Failing here beats failing ten minutes into a build.
raise SpecError(
"[nix] flake = true needs shim = true -- see ../README.md"
)
if self.use_shim and not os.path.exists(PTYSHIM_C):
raise SpecError(f"[nix] shim = true but {PTYSHIM_C} is missing")
if self.ports and self.runtime != "sandbox":
raise SpecError(
"[network] ports needs [container] runtime = \"sandbox\" --"
" a Function has no process to tunnel into"
)
for name, mount in self.volume_spec.items():
if not isinstance(mount, str) or not mount.startswith("/"):
raise SpecError(
f"[volumes] {name} must be an absolute path, not {mount!r}"
)
# Mounting over one of these hides what the image already has
# there -- /nix in particular, where the empty volume would shadow
# the store the base image spent its build populating.
if mount.rstrip("/") in ("", "/nix", "/nix/store", "/usr", "/etc"):
raise SpecError(
f"[volumes] {name} may not mount over {mount} --"
" it would hide what the image has there"
)
if mount.rstrip("/") == self.workdir.rstrip("/"):
raise SpecError(
f"[volumes] {name} may not mount over the workdir"
f" ({mount}) -- [build] include copies land there"
)
# -- image -----------------------------------------------------------
@property
def nix(self) -> str:
"""The `nix` command as the container runs it.
A sandbox on a real VM has a working pty, so the shim buys nothing
there and is left off even when the image was built with it.
"""
if self.use_shim and not self.vm_at_runtime:
return f"LD_PRELOAD={SHIM_SO} nix"
return "nix"
@property
def vm_at_runtime(self) -> bool:
"""True when this container actually runs on a VM rather than gVisor."""
return (self.runtime == "sandbox"
and bool(self.experimental_options.get("vm_runtime")))
@property
def build_nix(self) -> str:
"""The `nix` command for BUILD steps, which always run under gVisor.
Image builds are Functions underneath, so a sandbox container still
needs the shim while its image is being built -- only its run time
gets the VM.
"""
return f"LD_PRELOAD={SHIM_SO} nix" if self.use_shim else "nix"
def _build_image(self) -> modal.Image:
c = self.spec["container"]
build = self.spec.get("build", {})
if c.get("base"):
image = modal.Image.from_name(c["base"])
else:
image = modal.Image.from_registry(c["registry"])
# `nix profile install` puts things in ~/.nix-profile/bin, which is on
# nobody's PATH here -- so the install succeeds and the very next line
# says `command not found`. Set on the image rather than in a .bashrc,
# because a container's command runs under `sh -c` and reads neither.
# Spelled out rather than prefixed onto $PATH: an image env is a value,
# not a shell expression, so "$PATH" here would be four literal
# characters.
image = image.env({
"PATH": "/root/.nix-profile/bin:/usr/local/sbin:/usr/local/bin"
":/usr/sbin:/usr/bin:/sbin:/bin",
})
if self.use_shim:
image = image.add_local_file(
PTYSHIM_C, "/opt/ptyshim.c", copy=True
).run_commands(
f"gcc -shared -fPIC -O2 -o {SHIM_SO} /opt/ptyshim.c -ldl"
)
# Warm the devShell BEFORE the source is copied in. Everything the
# shell needs is binary-cached, so the download happens once -- but
# only if this layer survives. Copy the source first and any edit to
# any file invalidates the warm, and the whole closure is fetched
# again on every build. Only flake.nix and flake.lock go in here, so
# the layer is invalidated by a dependency change and nothing else.
if self.use_flake:
for f in ("flake.nix", "flake.lock"):
path = os.path.join(self.dir, f)
if os.path.exists(path):
image = image.add_local_file(
path, f"{self.workdir}/{f}", copy=True
)
image = image.run_commands(
f"cd {self.workdir} && {self.build_nix} develop"
" --accept-flake-config --command true",
f'echo "store paths after warming:'
f' $({self.build_nix} path-info --all | wc -l)"',
)
# copy=True throughout: later run_commands need these files present.
# `context` is what include paths are relative to, and it may sit above
# the container directory -- a container that builds the repo it lives
# in sets context = "../..", so include = ["."] means the whole repo.
context = os.path.normpath(os.path.join(self.dir, build.get("context", ".")))
# Image building and program building, kept apart.
#
# `[build] commands` run AFTER the source copy, so any edit anywhere in
# the tree invalidates them -- and for a container whose commands warm
# a devShell, that means minutes of nix on every iteration of a
# one-line change. `warm` + `setup` are the same two steps moved in
# front of the source: `warm` names only the files the flake actually
# evaluates (its own, and whatever the devShell's derivations read),
# and `setup` runs against those alone. Editing `flutter/src` then
# invalidates nothing above the final copy, and the toolchain layer is
# reused until a dependency moves.
#
# Volumes are mounted here for `commands`' reason: a step that can
# reach the binary cache never has to build, which is the one thing
# gVisor will not do.
for rel in build.get("warm", []):
src = os.path.normpath(os.path.join(context, rel))
dest = f"{self.workdir}/{rel}"
if os.path.isdir(src):
image = image.add_local_dir(src, dest, copy=True)
else:
image = image.add_local_file(src, dest, copy=True)
if setup := build.get("setup", []):
image = image.run_commands(*setup, volumes=self.volumes)
# `ignore` is what keeps a build tree out of the image. A checkout that
# has been built in locally carries its output -- flutter/build and the
# caches beside it were 395MB of a 441MB repo -- and all of it would be
# uploaded on every start only to be thrown away, since the container
# builds into a volume of its own. Patterns are relative to the copied
# directory, as in .dockerignore.
ignore = list(build.get("ignore", []))
for rel in build.get("include", ["."]):
src = os.path.normpath(os.path.join(context, rel))
dest = self.workdir if rel == "." else f"{self.workdir}/{rel}"
if os.path.isdir(src):
image = image.add_local_dir(src, dest, copy=True, ignore=ignore)
else:
image = image.add_local_file(src, dest, copy=True)
# A repo copied in brings its `.git` along, and in a worktree that is a
# *file* holding `gitdir: <path on the machine that copied it>`. Nix
# believes it and goes looking for a checkout that is not there --
# `nix develop` and `nix build .#x` both die before evaluating
# anything. Nothing in a container wants the git metadata, so it goes.
image = image.run_commands(f"rm -rf {self.workdir}/.git")
if commands := build.get("commands", []):
# Volumes mounted for the build too, not just the run. A build step
# that wants nix to *build* something is the one thing gVisor will
# not do -- image builds are Functions underneath, and a derivation
# there dies on `unexpected EOF reading a line`. Substituting is
# fine, so a step that can reach the cache never has to build, and
# the shim stays retired. The mount is not part of the resulting
# image; only what the step writes outside it is.
image = image.run_commands(*commands, volumes=self.volumes)
# container.py does `from _loader import Container`, and Modal mounts
# the entrypoint file alone -- so without this the import that works
# locally fails in the container. copy=False adds it at startup rather
# than baking a layer, so it invalidates nothing above it, and it must
# therefore come after every build step.
image = image.add_local_python_source("_loader")
# ...and container.py reads its spec at import time, so the spec has to
# be there too. Modal re-imports the entrypoint at /root, which is the
# one directory that gets none of the workdir copies above.
image = image.add_local_file(
os.path.join(self.dir, "container.toml"), "/root/container.toml"
)
return image
# -- volumes ---------------------------------------------------------
@property
def volumes(self) -> dict:
"""{mount path: Volume}, as both Sandbox.create and @app.function want.
`from_name` is lazy, so this is safe to evaluate on the re-import
inside the container as well as out here. create_if_missing means a
spec naming a volume that does not exist yet makes it rather than
failing -- the first run of a cache is the one that fills it.
"""
return {
mount: modal.Volume.from_name(name, create_if_missing=True)
for name, mount in self.volume_spec.items()
}
# -- function --------------------------------------------------------
@property
def function_kwargs(self) -> dict:
"""Everything `@app.function` should be given, from [resources]."""
r = self.spec.get("resources", {})
kwargs: dict = {"timeout": int(r.get("timeout", 900))}
if r.get("cpu"):
kwargs["cpu"] = float(r["cpu"])
if r.get("memory"):
kwargs["memory"] = int(r["memory"])
if r.get("gpu"):
kwargs["gpu"] = r["gpu"]
# Deliberately NOT self.experimental_options: that fills in the
# sandbox default, and vm_runtime on a Function is refused by the
# server. A sandbox container's @app.function is vestigial anyway.
if self.runtime == "function":
if experimental := dict(self.spec.get("experimental", {})):
kwargs["experimental_options"] = experimental
if volumes := self.volumes:
kwargs["volumes"] = volumes
return kwargs
@property
def experimental_options(self) -> dict:
"""Experimental options, with the sandbox default filled in.
`vm_runtime` is Sandbox-only: the server rejects it on a Function
outright. So it is defaulted on for sandboxes and never for functions,
and an explicit [experimental] table always wins.
"""
explicit = dict(self.spec.get("experimental", {}))
if explicit:
return explicit
if self.runtime == "sandbox":
return {"vm_runtime": True}
return {}
@property
def sandbox_kwargs(self) -> dict:
"""Everything `Sandbox.create` should be given, from [resources]."""
r = self.spec.get("resources", {})
kwargs: dict = {"timeout": int(r.get("timeout", 900))}
if r.get("cpu"):
kwargs["cpu"] = float(r["cpu"])
if r.get("memory"):
# A VM sandbox gets exactly this much and cannot grow into more.
kwargs["memory"] = int(r["memory"])
if opts := self.experimental_options:
kwargs["experimental_options"] = dict(opts)
if volumes := self.volumes:
kwargs["volumes"] = volumes
if self.ports:
kwargs["encrypted_ports"] = list(self.ports)
return kwargs
def shell_command(self, override: str = "") -> str:
"""The full shell line the container runs, devShell wrapper included."""
command = override or self.command
if not command:
raise SpecError("container.toml has no [run] command")
if self.use_flake:
return (
f"cd {self.workdir} && {self.nix} develop --accept-flake-config"
f" --command sh -c {shlex.quote(command)}"
)
return f"cd {self.workdir} && {command}"
def run_sandbox(self, override: str = "") -> str:
"""Run one command in a Sandbox that dies when the command does.
The command IS the sandbox's process, rather than something exec'd
into a `sleep infinity` box that then has to be torn down. There is no
idle window to pay for and nothing to leak if this script is killed;
the [resources] timeout is a backstop, not the mechanism.
Modal streams a Sandbox's output into the app log as it runs -- which
is what you want for a build -- so this returns "" rather than handing
back a copy for the caller to print underneath it.
"""
line = self.shell_command(override)
sb = modal.Sandbox.create(
"sh", "-c", line,
app=self.app,
image=self.image,
workdir=self.workdir,
env={k: str(v) for k, v in self.env.items()},
**self.sandbox_kwargs,
)
self._print_tunnels(sb)
sb.wait()
if sb.returncode != 0:
raise RuntimeError(
f"{self.name}: command failed ({sb.returncode})\n"
f"$ {line}\n{sb.stderr.read()}"
)
return ""
def _print_tunnels(self, sb: "modal.Sandbox") -> None:
"""Say where a tunnelled port can be reached, once the sandbox is up.
`tunnels()` blocks until the Sandbox is scheduled, which is why this
is called after create and not folded into it. Nothing prints when
[network] ports is empty, which is every container but the serving
ones.
"""
if not self.ports:
return
for port, tunnel in sb.tunnels().items():
print(f" :{port} -> {tunnel.url}")
def open_sandbox(self) -> "modal.Sandbox":
"""Start a Sandbox and leave it running, for `scripts/shell`.
Same workdir and the same [run] env as the real thing: a shell opened
to debug a container that does not have the container's environment is
a shell that reproduces something else. `command` is the one part left
out, because not running it is the point.
"""
return modal.Sandbox.create(
"sleep",
"infinity",
app=self.app,
image=self.image,
workdir=self.workdir,
env={k: str(v) for k, v in self.env.items()},
**self.sandbox_kwargs,
)
def execute(self, override: str = "") -> str:
"""Run the command in this container. Called remotely, not locally."""
line = self.shell_command(override)
result = subprocess.run(
line,
shell=True,
capture_output=True,
text=True,
env={**os.environ, **{k: str(v) for k, v in self.env.items()}},
)
if result.returncode != 0:
raise RuntimeError(
f"{self.name}: command failed ({result.returncode})\n"
f"$ {line}\n{result.stderr}"
)
return result.stdout
|