161 lines
4.6 KiB
Markdown
161 lines
4.6 KiB
Markdown
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# Buildah Tutorial 4
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## Include Buildah in your build tool
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The purpose of this tutorial is to demonstrate how to include Buildah as a library in your build tool.
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You can take advantage of all features provided by Buildah, like using Dockerfiles and building using rootless mode.
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In this tutorial I'll show you how to create a simple CLI tool that creates an image containing NodeJS and a JS main file.
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## Bootstrap the project and install the dependencies
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Bootstrap the installation of development dependencies of Buildah by following the [Building from scratch](https://github.com/slinkydeveloper/buildah/blob/master/install.md#building-from-scratch) instructions and in particular creating a directory for the Buildah project by completing the instructions in the [Installation from GitHub](https://github.com/containers/buildah/blob/master/install.md#installation-from-github) section of that page.
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Now let's bootstrap our project. Assuming you are in the directory of the project, run:
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```shell
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go mod init
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```
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To initialize the go modules. Now import Buildah as a dependency:
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```shell
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go get github.com/containers/buildah
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```
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## Build the image
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Now you can develop your application. To access to the build features of Buildah, you need to instantiate `buildah.Builder`. This struct has methods to configure the build, define the build steps and run it.
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To instantiate a `Builder`, you need a `storage.Store` (the Store interface found in [store.go](https://github.com/containers/storage/blob/master/store.go)) from [`github.com/containers/storage`](https://github.com/containers/storage), where the intermediate and result images will be stored:
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```go
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buildStoreOptions, err := storage.DefaultStoreOptions(unshare.IsRootless(), unshare.GetRootlessUID())
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buildStore, err := storage.GetStore(buildStoreOptions)
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```
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Define the builder options:
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```go
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builderOpts := buildah.BuilderOptions{
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FromImage: "node:12-alpine", // Starting image
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Isolation: buildah.IsolationChroot, // Isolation environment
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CommonBuildOpts: &buildah.CommonBuildOptions{},
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ConfigureNetwork: buildah.NetworkDefault,
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SystemContext: &types.SystemContext {},
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}
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```
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Now instantiate the `Builder`:
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```go
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builder, err := buildah.NewBuilder(context.TODO(), buildStore, builderOpts)
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```
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Let's add our JS file (assuming is in your local directory with name `script.js`):
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```go
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err = builder.Add("/home/node/", false, buildah.AddAndCopyOptions{}, "script.js")
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```
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And configure the command to run:
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```go
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builder.SetCmd([]string{"node", "/home/node/script.js"})
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```
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Before completing the build, create the image reference:
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```go
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imageRef, err := is.Transport.ParseStoreReference(buildStore, "docker.io/myusername/my-image")
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```
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Now you can run commit the build:
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```go
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imageId, _, _, err := builder.Commit(context.TODO(), imageRef, buildah.CommitOptions{})
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```
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## Rootless mode
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To enable rootless mode, import `github.com/containers/common/pkg/unshare` and add this code at the beginning of your main method:
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```go
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if buildah.InitReexec() {
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return
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}
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unshare.MaybeReexecUsingUserNamespace(false)
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```
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This code ensures that your application is re executed in an isolated environment with root privileges.
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## Complete code
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```go
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package main
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import (
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"context"
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"fmt"
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"github.com/containers/buildah"
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"github.com/containers/common/pkg/unshare"
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is "github.com/containers/image/v5/storage"
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"github.com/containers/image/v5/types"
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"github.com/containers/storage"
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)
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func main() {
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if buildah.InitReexec() {
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return
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}
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unshare.MaybeReexecUsingUserNamespace(false)
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buildStoreOptions, err := storage.DefaultStoreOptions(unshare.IsRootless(), unshare.GetRootlessUID())
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if err != nil {
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panic(err)
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}
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buildStore, err := storage.GetStore(buildStoreOptions)
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if err != nil {
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panic(err)
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}
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opts := buildah.BuilderOptions{
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FromImage: "node:12-alpine",
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Isolation: buildah.IsolationChroot,
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CommonBuildOpts: &buildah.CommonBuildOptions{},
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ConfigureNetwork: buildah.NetworkDefault,
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SystemContext: &types.SystemContext {},
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}
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builder, err := buildah.NewBuilder(context.TODO(), buildStore, opts)
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if err != nil {
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panic(err)
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}
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err = builder.Add("/home/node/", false, buildah.AddAndCopyOptions{}, "script.js")
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if err != nil {
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panic(err)
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}
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builder.SetCmd([]string{"node", "/home/node/script.js"})
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imageRef, err := is.Transport.ParseStoreReference(buildStore, "docker.io/myusername/my-image")
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if err != nil {
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panic(err)
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}
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imageId, _, _, err := builder.Commit(context.TODO(), imageRef, buildah.CommitOptions{})
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fmt.Printf("Image built! %s\n", imageId)
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}
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```
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