119af77b43
Uses the structured errors feature introduced in the Nix code to return more sensible errors to clients. For now this is quite limited, but already a lot better than before: * packages that could not be found result in 404s * all other errors result in 500s This way the registry clients will not attempt to interpret the returned garbage data/empty response as something useful.
432 lines
13 KiB
Go
432 lines
13 KiB
Go
// Copyright 2019 Google LLC
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//
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// Licensed under the Apache License, Version 2.0 (the "License"); you may not
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// use this file except in compliance with the License. You may obtain a copy of
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// the License at
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//
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// https://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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// WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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// License for the specific language governing permissions and limitations under
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// the License.
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// Package main provides the implementation of a container registry that
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// transparently builds container images based on Nix derivations.
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//
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// The Nix derivation used for image creation is responsible for creating
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// objects that are compatible with the registry API. The targeted registry
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// protocol is currently Docker's.
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//
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// When an image is requested, the required contents are parsed out of the
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// request and a Nix-build is initiated that eventually responds with the
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// manifest as well as information linking each layer digest to a local
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// filesystem path.
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//
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// Nixery caches the filesystem paths and returns the manifest to the client.
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// Subsequent requests for layer content per digest are then fulfilled by
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// serving the files from disk.
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package main
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import (
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"bytes"
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"context"
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"encoding/json"
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"fmt"
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"io"
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"io/ioutil"
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"log"
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"net/http"
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"os"
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"os/exec"
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"regexp"
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"strings"
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"cloud.google.com/go/storage"
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)
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// pkgSource represents the source from which the Nix package set used
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// by Nixery is imported. Users configure the source by setting one of
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// the supported environment variables.
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type pkgSource struct {
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srcType string
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args string
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}
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// Convert the package source into the representation required by Nix.
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func (p *pkgSource) renderSource(tag string) string {
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// The 'git' source requires a tag to be present.
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if p.srcType == "git" {
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if tag == "latest" || tag == "" {
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tag = "master"
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}
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return fmt.Sprintf("git!%s!%s", p.args, tag)
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}
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return fmt.Sprintf("%s!%s", p.srcType, p.args)
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}
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// Retrieve a package source from the environment. If no source is
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// specified, the Nix code will default to a recent NixOS channel.
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func pkgSourceFromEnv() *pkgSource {
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if channel := os.Getenv("NIXERY_CHANNEL"); channel != "" {
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log.Printf("Using Nix package set from Nix channel %q\n", channel)
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return &pkgSource{
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srcType: "nixpkgs",
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args: channel,
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}
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}
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if git := os.Getenv("NIXERY_PKGS_REPO"); git != "" {
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log.Printf("Using Nix package set from git repository at %q\n", git)
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return &pkgSource{
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srcType: "git",
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args: git,
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}
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}
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if path := os.Getenv("NIXERY_PKGS_PATH"); path != "" {
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log.Printf("Using Nix package set from path %q\n", path)
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return &pkgSource{
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srcType: "path",
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args: path,
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}
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}
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return nil
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}
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// config holds the Nixery configuration options.
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type config struct {
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bucket string // GCS bucket to cache & serve layers
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builder string // Nix derivation for building images
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web string // Static files to serve over HTTP
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port string // Port on which to launch HTTP server
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pkgs *pkgSource // Source for Nix package set
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}
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// ManifestMediaType is the Content-Type used for the manifest itself. This
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// corresponds to the "Image Manifest V2, Schema 2" described on this page:
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//
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// https://docs.docker.com/registry/spec/manifest-v2-2/
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const manifestMediaType string = "application/vnd.docker.distribution.manifest.v2+json"
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// Image represents the information necessary for building a container image.
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// This can be either a list of package names (corresponding to keys in the
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// nixpkgs set) or a Nix expression that results in a *list* of derivations.
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type image struct {
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// Name of the container image.
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name string
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// Tag requested (only relevant for package sets from git repositories)
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tag string
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// Names of packages to include in the image. These must correspond
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// directly to top-level names of Nix packages in the nixpkgs tree.
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packages []string
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}
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// BuildResult represents the output of calling the Nix derivation responsible
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// for building registry images.
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//
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// The `layerLocations` field contains the local filesystem paths to each
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// individual image layer that will need to be served, while the `manifest`
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// field contains the JSON-representation of the manifest that needs to be
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// served to the client.
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//
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// The later field is simply treated as opaque JSON and passed through.
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type BuildResult struct {
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Error string `json:"error`
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Pkgs []string `json:"pkgs"`
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Manifest json.RawMessage `json:"manifest"`
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LayerLocations map[string]struct {
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Path string `json:"path"`
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Md5 []byte `json:"md5"`
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} `json:"layerLocations"`
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}
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// imageFromName parses an image name into the corresponding structure which can
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// be used to invoke Nix.
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//
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// It will expand convenience names under the hood (see the `convenienceNames`
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// function below).
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func imageFromName(name string, tag string) image {
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packages := strings.Split(name, "/")
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return image{
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name: name,
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tag: tag,
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packages: convenienceNames(packages),
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}
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}
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// convenienceNames expands convenience package names defined by Nixery which
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// let users include commonly required sets of tools in a container quickly.
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//
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// Convenience names must be specified as the first package in an image.
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//
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// Currently defined convenience names are:
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//
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// * `shell`: Includes bash, coreutils and other common command-line tools
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// * `builder`: All of the above and the standard build environment
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func convenienceNames(packages []string) []string {
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shellPackages := []string{"bashInteractive", "coreutils", "moreutils", "nano"}
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builderPackages := append(shellPackages, "stdenv")
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if packages[0] == "shell" {
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return append(packages[1:], shellPackages...)
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} else if packages[0] == "builder" {
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return append(packages[1:], builderPackages...)
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} else {
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return packages
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}
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}
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// Call out to Nix and request that an image be built. Nix will, upon success,
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// return a manifest for the container image.
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func buildImage(ctx *context.Context, cfg *config, image *image, bucket *storage.BucketHandle) (*BuildResult, error) {
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packages, err := json.Marshal(image.packages)
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if err != nil {
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return nil, err
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}
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args := []string{
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"--no-out-link",
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"--show-trace",
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"--argstr", "name", image.name,
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"--argstr", "packages", string(packages), cfg.builder,
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}
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if cfg.pkgs != nil {
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args = append(args, "--argstr", "pkgSource", cfg.pkgs.renderSource(image.tag))
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}
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cmd := exec.Command("nix-build", args...)
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outpipe, err := cmd.StdoutPipe()
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if err != nil {
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return nil, err
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}
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errpipe, err := cmd.StderrPipe()
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if err != nil {
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return nil, err
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}
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if err = cmd.Start(); err != nil {
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log.Println("Error starting nix-build:", err)
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return nil, err
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}
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log.Printf("Started Nix image build for '%s'", image.name)
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stdout, _ := ioutil.ReadAll(outpipe)
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stderr, _ := ioutil.ReadAll(errpipe)
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if err = cmd.Wait(); err != nil {
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// TODO(tazjin): Propagate errors upwards in a usable format.
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log.Printf("nix-build execution error: %s\nstdout: %s\nstderr: %s\n", err, stdout, stderr)
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return nil, err
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}
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log.Println("Finished Nix image build")
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buildOutput, err := ioutil.ReadFile(strings.TrimSpace(string(stdout)))
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if err != nil {
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return nil, err
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}
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// The build output returned by Nix is deserialised to add all
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// contained layers to the bucket. Only the manifest itself is
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// re-serialised to JSON and returned.
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var result BuildResult
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err = json.Unmarshal(buildOutput, &result)
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if err != nil {
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return nil, err
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}
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for layer, meta := range result.LayerLocations {
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err = uploadLayer(ctx, bucket, layer, meta.Path, meta.Md5)
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if err != nil {
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return nil, err
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}
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}
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return &result, nil
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}
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// uploadLayer uploads a single layer to Cloud Storage bucket. Before writing
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// any data the bucket is probed to see if the file already exists.
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//
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// If the file does exist, its MD5 hash is verified to ensure that the stored
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// file is not - for example - a fragment of a previous, incomplete upload.
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func uploadLayer(ctx *context.Context, bucket *storage.BucketHandle, layer string, path string, md5 []byte) error {
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layerKey := fmt.Sprintf("layers/%s", layer)
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obj := bucket.Object(layerKey)
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// Before uploading a layer to the bucket, probe whether it already
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// exists.
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//
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// If it does and the MD5 checksum matches the expected one, the layer
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// upload can be skipped.
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attrs, err := obj.Attrs(*ctx)
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if err == nil && bytes.Equal(attrs.MD5, md5) {
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log.Printf("Layer sha256:%s already exists in bucket, skipping upload", layer)
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} else {
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writer := obj.NewWriter(*ctx)
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file, err := os.Open(path)
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if err != nil {
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return fmt.Errorf("failed to open layer %s from path %s: %v", layer, path, err)
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}
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size, err := io.Copy(writer, file)
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if err != nil {
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return fmt.Errorf("failed to write layer %s to Cloud Storage: %v", layer, err)
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}
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if err = writer.Close(); err != nil {
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return fmt.Errorf("failed to write layer %s to Cloud Storage: %v", layer, err)
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}
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log.Printf("Uploaded layer sha256:%s (%v bytes written)\n", layer, size)
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}
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return nil
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}
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// layerRedirect constructs the public URL of the layer object in the Cloud
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// Storage bucket and redirects the client there.
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//
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// The Docker client is known to follow redirects, but this might not be true
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// for all other registry clients.
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func layerRedirect(w http.ResponseWriter, cfg *config, digest string) {
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log.Printf("Redirecting layer '%s' request to bucket '%s'\n", digest, cfg.bucket)
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url := fmt.Sprintf("https://storage.googleapis.com/%s/layers/%s", cfg.bucket, digest)
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w.Header().Set("Location", url)
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w.WriteHeader(303)
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}
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// prepareBucket configures the handle to a Cloud Storage bucket in which
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// individual layers will be stored after Nix builds. Nixery does not directly
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// serve layers to registry clients, instead it redirects them to the public
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// URLs of the Cloud Storage bucket.
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//
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// The bucket is required for Nixery to function correctly, hence fatal errors
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// are generated in case it fails to be set up correctly.
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func prepareBucket(ctx *context.Context, cfg *config) *storage.BucketHandle {
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client, err := storage.NewClient(*ctx)
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if err != nil {
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log.Fatalln("Failed to set up Cloud Storage client:", err)
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}
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bkt := client.Bucket(cfg.bucket)
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if _, err := bkt.Attrs(*ctx); err != nil {
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log.Fatalln("Could not access configured bucket", err)
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}
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return bkt
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}
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// Regexes matching the V2 Registry API routes. This only includes the
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// routes required for serving images, since pushing and other such
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// functionality is not available.
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var (
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manifestRegex = regexp.MustCompile(`^/v2/([\w|\-|\.|\_|\/]+)/manifests/([\w|\-|\.|\_]+)$`)
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layerRegex = regexp.MustCompile(`^/v2/([\w|\-|\.|\_|\/]+)/blobs/sha256:(\w+)$`)
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)
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func getConfig(key, desc string) string {
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value := os.Getenv(key)
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if value == "" {
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log.Fatalln(desc + " must be specified")
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}
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return value
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}
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type registryHandler struct {
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cfg *config
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ctx *context.Context
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bucket *storage.BucketHandle
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}
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func (h *registryHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
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// Serve the manifest (straight from Nix)
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manifestMatches := manifestRegex.FindStringSubmatch(r.RequestURI)
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if len(manifestMatches) == 3 {
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imageName := manifestMatches[1]
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imageTag := manifestMatches[2]
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log.Printf("Requesting manifest for image %q at tag %q", imageName, imageTag)
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image := imageFromName(imageName, imageTag)
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buildResult, err := buildImage(h.ctx, h.cfg, &image, h.bucket)
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if err != nil {
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log.Println("Failed to build image manifest", err)
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w.WriteHeader(500)
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return
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}
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// Some error types have special handling, which is applied
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// here.
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if buildResult.Error == "not_found" {
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log.Printf("Could not find packages: %v\n", buildResult.Pkgs)
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w.WriteHeader(404)
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return
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}
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// This marshaling error is ignored because we know that this
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// field represents valid JSON data.
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manifest, _ := json.Marshal(buildResult.Manifest)
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w.Header().Add("Content-Type", manifestMediaType)
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w.Write(manifest)
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return
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}
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// Serve an image layer. For this we need to first ask Nix for
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// the manifest, then proceed to extract the correct layer from
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// it.
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layerMatches := layerRegex.FindStringSubmatch(r.RequestURI)
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if len(layerMatches) == 3 {
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digest := layerMatches[2]
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layerRedirect(w, h.cfg, digest)
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return
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}
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log.Printf("Unsupported registry route: %s\n", r.RequestURI)
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w.WriteHeader(404)
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}
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func main() {
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cfg := &config{
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bucket: getConfig("BUCKET", "GCS bucket for layer storage"),
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builder: getConfig("NIX_BUILDER", "Nix image builder code"),
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web: getConfig("WEB_DIR", "Static web file dir"),
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port: getConfig("PORT", "HTTP port"),
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pkgs: pkgSourceFromEnv(),
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}
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ctx := context.Background()
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bucket := prepareBucket(&ctx, cfg)
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log.Printf("Starting Kubernetes Nix controller on port %s\n", cfg.port)
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// Acknowledge that we speak V2
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http.HandleFunc("/v2", func(w http.ResponseWriter, r *http.Request) {
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fmt.Fprintln(w)
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})
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// All other /v2/ requests belong to the registry handler.
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http.Handle("/v2/", ®istryHandler{
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cfg: cfg,
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ctx: &ctx,
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bucket: bucket,
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})
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// All other roots are served by the static file server.
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http.Handle("/", http.FileServer(http.Dir(cfg.web)))
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log.Fatal(http.ListenAndServe(":"+cfg.port, nil))
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}
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