diff options
Diffstat (limited to 'tools/nixery/build-image')
| -rw-r--r-- | tools/nixery/build-image/build-image.nix | 4 | ||||
| -rw-r--r-- | tools/nixery/build-image/default.nix | 96 | ||||
| -rw-r--r-- | tools/nixery/build-image/go-deps.nix | 10 | ||||
| -rw-r--r-- | tools/nixery/build-image/group-layers.go | 352 |
4 files changed, 18 insertions, 444 deletions
diff --git a/tools/nixery/build-image/build-image.nix b/tools/nixery/build-image/build-image.nix index 1d97ba59b97d..33500dbb9e80 100644 --- a/tools/nixery/build-image/build-image.nix +++ b/tools/nixery/build-image/build-image.nix @@ -26,6 +26,8 @@ srcType ? "nixpkgs", srcArgs ? "nixos-19.03", importArgs ? { }, + # Path to load-pkgs.nix + loadPkgs ? ./load-pkgs.nix, # Packages to install by name (which must refer to top-level attributes of # nixpkgs). This is passed in as a JSON-array in string form. packages ? "[]" @@ -43,7 +45,7 @@ let inherit (pkgs) lib runCommand writeText; - pkgs = import ./load-pkgs.nix { inherit srcType srcArgs importArgs; }; + pkgs = import loadPkgs { inherit srcType srcArgs importArgs; }; # deepFetch traverses the top-level Nix package set to retrieve an item via a # path specified in string form. diff --git a/tools/nixery/build-image/default.nix b/tools/nixery/build-image/default.nix index 3bb5d62fb0d5..a61ac06bdd92 100644 --- a/tools/nixery/build-image/default.nix +++ b/tools/nixery/build-image/default.nix @@ -12,84 +12,18 @@ # See the License for the specific language governing permissions and # limitations under the License. -# This file builds the tool used to calculate layer distribution and -# moves the files needed to call the Nix builds at runtime in the -# correct locations. - -{ pkgs ? null, self ? ./. - - # Because of the insanity occuring below, this function must mirror - # all arguments of build-image.nix. -, srcType ? "nixpkgs" -, srcArgs ? "nixos-19.03" -, tag ? null, name ? null, packages ? null, maxLayers ? null, popularityUrl ? null -}@args: - -let pkgs = import ./load-pkgs.nix { inherit srcType srcArgs; }; -in with pkgs; rec { - - groupLayers = buildGoPackage { - name = "group-layers"; - goDeps = ./go-deps.nix; - goPackagePath = "github.com/google/nixery/group-layers"; - - # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # - # WARNING: HERE BE DRAGONS! # - # # - # The hack below is used to break evaluation purity. The issue is # - # that Nixery's build instructions (the default.nix in the folder # - # above this one) must build a program that can invoke Nix at # - # runtime, with a derivation that needs a program tracked in this # - # source tree (`group-layers`). # - # # - # Simply installing that program in the $PATH of Nixery does not # - # work, because the runtime Nix builds use their own isolated # - # environment. # - # # - # I first attempted to naively copy the sources into the Nix # - # store, so that Nixery could build `group-layers` when it starts # - # up - however those sources are not available to a nested Nix # - # build because they're not part of the context of the nested # - # invocation. # - # # - # Nix has several primitives under `builtins.` that can break # - # evaluation purity, these (namely readDir and readFile) are used # - # below to break out of the isolated environment and reconstruct # - # the source tree for `group-layers`. # - # # - # There might be a better way to do this, but I don't know what # - # it is. # - # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # # - src = runCommand "group-layers-srcs" { } '' - mkdir -p $out - ${with builtins; - let - files = - (attrNames (lib.filterAttrs (_: t: t != "symlink") (readDir self))); - commands = - map (f: "cp ${toFile f (readFile "${self}/${f}")} $out/${f}") files; - in lib.concatStringsSep "\n" commands} - ''; - - meta = { - description = - "Tool to group a set of packages into container image layers"; - license = lib.licenses.asl20; - maintainers = [ lib.maintainers.tazjin ]; - }; - }; - - buildImage = import ./build-image.nix - ({ inherit pkgs groupLayers; } // (lib.filterAttrs (_: v: v != null) args)); - - # Wrapper script which is called by the Nixery server to trigger an - # actual image build. This exists to avoid having to specify the - # location of build-image.nix at runtime. - wrapper = writeShellScriptBin "nixery-build-image" '' - exec ${nix}/bin/nix-build \ - --show-trace \ - --no-out-link "$@" \ - --argstr self "${./.}" \ - -A buildImage ${./.} - ''; -} +# This file builds a wrapper script called by Nixery to ask for the +# content information for a given image. +# +# The purpose of using a wrapper script is to ensure that the paths to +# all required Nix files are set correctly at runtime. + +{ pkgs ? import <nixpkgs> {} }: + +pkgs.writeShellScriptBin "nixery-build-image" '' + exec ${pkgs.nix}/bin/nix-build \ + --show-trace \ + --no-out-link "$@" \ + --argstr loadPkgs ${./load-pkgs.nix} \ + ${./build-image.nix} +'' diff --git a/tools/nixery/build-image/go-deps.nix b/tools/nixery/build-image/go-deps.nix deleted file mode 100644 index 0f22a7088f52..000000000000 --- a/tools/nixery/build-image/go-deps.nix +++ /dev/null @@ -1,10 +0,0 @@ -# This file was generated by https://github.com/kamilchm/go2nix v1.3.0 -[{ - goPackagePath = "gonum.org/v1/gonum"; - fetch = { - type = "git"; - url = "https://github.com/gonum/gonum"; - rev = "ced62fe5104b907b6c16cb7e575c17b2e62ceddd"; - sha256 = "1b7q6haabnp53igpmvr6a2414yralhbrldixx4kbxxg1apy8jdjg"; - }; -}] diff --git a/tools/nixery/build-image/group-layers.go b/tools/nixery/build-image/group-layers.go deleted file mode 100644 index 93f2e520ace9..000000000000 --- a/tools/nixery/build-image/group-layers.go +++ /dev/null @@ -1,352 +0,0 @@ -// This program reads an export reference graph (i.e. a graph representing the -// runtime dependencies of a set of derivations) created by Nix and groups them -// in a way that is likely to match the grouping for other derivation sets with -// overlapping dependencies. -// -// This is used to determine which derivations to include in which layers of a -// container image. -// -// # Inputs -// -// * a graph of Nix runtime dependencies, generated via exportReferenceGraph -// * a file containing absolute popularity values of packages in the -// Nix package set (in the form of a direct reference count) -// * a maximum number of layers to allocate for the image (the "layer budget") -// -// # Algorithm -// -// It works by first creating a (directed) dependency tree: -// -// img (root node) -// │ -// ├───> A ─────┐ -// │ v -// ├───> B ───> E -// │ ^ -// ├───> C ─────┘ -// │ │ -// │ v -// └───> D ───> F -// │ -// └────> G -// -// Each node (i.e. package) is then visited to determine how important -// it is to separate this node into its own layer, specifically: -// -// 1. Is the node within a certain threshold percentile of absolute -// popularity within all of nixpkgs? (e.g. `glibc`, `openssl`) -// -// 2. Is the node's runtime closure above a threshold size? (e.g. 100MB) -// -// In either case, a bit is flipped for this node representing each -// condition and an edge to it is inserted directly from the image -// root, if it does not already exist. -// -// For the rest of the example we assume 'G' is above the threshold -// size and 'E' is popular. -// -// This tree is then transformed into a dominator tree: -// -// img -// │ -// ├───> A -// ├───> B -// ├───> C -// ├───> E -// ├───> D ───> F -// └───> G -// -// Specifically this means that the paths to A, B, C, E, G, and D -// always pass through the root (i.e. are dominated by it), whilst F -// is dominated by D (all paths go through it). -// -// The top-level subtrees are considered as the initially selected -// layers. -// -// If the list of layers fits within the layer budget, it is returned. -// -// Otherwise, a merge rating is calculated for each layer. This is the -// product of the layer's total size and its root node's popularity. -// -// Layers are then merged in ascending order of merge ratings until -// they fit into the layer budget. -// -// # Threshold values -// -// Threshold values for the partitioning conditions mentioned above -// have not yet been determined, but we will make a good first guess -// based on gut feeling and proceed to measure their impact on cache -// hits/misses. -// -// # Example -// -// Using the logic described above as well as the example presented in -// the introduction, this program would create the following layer -// groupings (assuming no additional partitioning): -// -// Layer budget: 1 -// Layers: { A, B, C, D, E, F, G } -// -// Layer budget: 2 -// Layers: { G }, { A, B, C, D, E, F } -// -// Layer budget: 3 -// Layers: { G }, { E }, { A, B, C, D, F } -// -// Layer budget: 4 -// Layers: { G }, { E }, { D, F }, { A, B, C } -// -// ... -// -// Layer budget: 10 -// Layers: { E }, { D, F }, { A }, { B }, { C } -package main - -import ( - "encoding/json" - "flag" - "io/ioutil" - "log" - "regexp" - "sort" - - "gonum.org/v1/gonum/graph/flow" - "gonum.org/v1/gonum/graph/simple" -) - -// closureGraph represents the structured attributes Nix outputs when asking it -// for the exportReferencesGraph of a list of derivations. -type exportReferences struct { - References struct { - Graph []string `json:"graph"` - } `json:"exportReferencesGraph"` - - Graph []struct { - Size uint64 `json:"closureSize"` - Path string `json:"path"` - Refs []string `json:"references"` - } `json:"graph"` -} - -// Popularity data for each Nix package that was calculated in advance. -// -// Popularity is a number from 1-100 that represents the -// popularity percentile in which this package resides inside -// of the nixpkgs tree. -type pkgsMetadata = map[string]int - -// layer represents the data returned for each layer that Nix should -// build for the container image. -type layer struct { - Contents []string `json:"contents"` - mergeRating uint64 -} - -func (a layer) merge(b layer) layer { - a.Contents = append(a.Contents, b.Contents...) - a.mergeRating += b.mergeRating - return a -} - -// closure as pointed to by the graph nodes. -type closure struct { - GraphID int64 - Path string - Size uint64 - Refs []string - Popularity int -} - -func (c *closure) ID() int64 { - return c.GraphID -} - -var nixRegexp = regexp.MustCompile(`^/nix/store/[a-z0-9]+-`) - -func (c *closure) DOTID() string { - return nixRegexp.ReplaceAllString(c.Path, "") -} - -// bigOrPopular checks whether this closure should be considered for -// separation into its own layer, even if it would otherwise only -// appear in a subtree of the dominator tree. -func (c *closure) bigOrPopular() bool { - const sizeThreshold = 100 * 1000000 // 100MB - - if c.Size > sizeThreshold { - return true - } - - // The threshold value used here is currently roughly the - // minimum number of references that only 1% of packages in - // the entire package set have. - // - // TODO(tazjin): Do this more elegantly by calculating - // percentiles for each package and using those instead. - if c.Popularity >= 1000 { - return true - } - - return false -} - -func insertEdges(graph *simple.DirectedGraph, cmap *map[string]*closure, node *closure) { - // Big or popular nodes get a separate edge from the top to - // flag them for their own layer. - if node.bigOrPopular() && !graph.HasEdgeFromTo(0, node.ID()) { - edge := graph.NewEdge(graph.Node(0), node) - graph.SetEdge(edge) - } - - for _, c := range node.Refs { - // Nix adds a self reference to each node, which - // should not be inserted. - if c != node.Path { - edge := graph.NewEdge(node, (*cmap)[c]) - graph.SetEdge(edge) - } - } -} - -// Create a graph structure from the references supplied by Nix. -func buildGraph(refs *exportReferences, pop *pkgsMetadata) *simple.DirectedGraph { - cmap := make(map[string]*closure) - graph := simple.NewDirectedGraph() - - // Insert all closures into the graph, as well as a fake root - // closure which serves as the top of the tree. - // - // A map from store paths to IDs is kept to actually insert - // edges below. - root := &closure{ - GraphID: 0, - Path: "image_root", - } - graph.AddNode(root) - - for idx, c := range refs.Graph { - node := &closure{ - GraphID: int64(idx + 1), // inc because of root node - Path: c.Path, - Size: c.Size, - Refs: c.Refs, - } - - if p, ok := (*pop)[node.DOTID()]; ok { - node.Popularity = p - } else { - node.Popularity = 1 - } - - graph.AddNode(node) - cmap[c.Path] = node - } - - // Insert the top-level closures with edges from the root - // node, then insert all edges for each closure. - for _, p := range refs.References.Graph { - edge := graph.NewEdge(root, cmap[p]) - graph.SetEdge(edge) - } - - for _, c := range cmap { - insertEdges(graph, &cmap, c) - } - - return graph -} - -// Extracts a subgraph starting at the specified root from the -// dominator tree. The subgraph is converted into a flat list of -// layers, each containing the store paths and merge rating. -func groupLayer(dt *flow.DominatorTree, root *closure) layer { - size := root.Size - contents := []string{root.Path} - children := dt.DominatedBy(root.ID()) - - // This iteration does not use 'range' because the list being - // iterated is modified during the iteration (yes, I'm sorry). - for i := 0; i < len(children); i++ { - child := children[i].(*closure) - size += child.Size - contents = append(contents, child.Path) - children = append(children, dt.DominatedBy(child.ID())...) - } - - return layer{ - Contents: contents, - // TODO(tazjin): The point of this is to factor in - // both the size and the popularity when making merge - // decisions, but there might be a smarter way to do - // it than a plain multiplication. - mergeRating: uint64(root.Popularity) * size, - } -} - -// Calculate the dominator tree of the entire package set and group -// each top-level subtree into a layer. -// -// Layers are merged together until they fit into the layer budget, -// based on their merge rating. -func dominate(budget int, graph *simple.DirectedGraph) []layer { - dt := flow.Dominators(graph.Node(0), graph) - - var layers []layer - for _, n := range dt.DominatedBy(dt.Root().ID()) { - layers = append(layers, groupLayer(&dt, n.(*closure))) - } - - sort.Slice(layers, func(i, j int) bool { - return layers[i].mergeRating < layers[j].mergeRating - }) - - if len(layers) > budget { - log.Printf("Ideal image has %v layers, but budget is %v\n", len(layers), budget) - } - - for len(layers) > budget { - merged := layers[0].merge(layers[1]) - layers[1] = merged - layers = layers[1:] - } - - return layers -} - -func main() { - graphFile := flag.String("graph", ".attrs.json", "Input file containing graph") - popFile := flag.String("pop", "popularity.json", "Package popularity data") - outFile := flag.String("out", "layers.json", "File to write layers to") - layerBudget := flag.Int("budget", 94, "Total layer budget available") - flag.Parse() - - // Parse graph data - file, err := ioutil.ReadFile(*graphFile) - if err != nil { - log.Fatalf("Failed to load input: %s\n", err) - } - - var refs exportReferences - err = json.Unmarshal(file, &refs) - if err != nil { - log.Fatalf("Failed to deserialise input: %s\n", err) - } - - // Parse popularity data - popBytes, err := ioutil.ReadFile(*popFile) - if err != nil { - log.Fatalf("Failed to load input: %s\n", err) - } - - var pop pkgsMetadata - err = json.Unmarshal(popBytes, &pop) - if err != nil { - log.Fatalf("Failed to deserialise input: %s\n", err) - } - - graph := buildGraph(&refs, &pop) - layers := dominate(*layerBudget, graph) - - j, _ := json.Marshal(layers) - ioutil.WriteFile(*outFile, j, 0644) -} |