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Proposal for new command "kustomize localize" (#4590)
* Propose kustomize localize Write mini KEP proposal for new command kustomize localize. * Incomplete commit * Update proposal based on Katrina's feedback Changes are summarized in comments in PR * Address feedback in comments
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| # Localize Command | ||
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| **Authors**: | ||
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| - annasong20 | ||
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| **Reviewers**: | ||
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| - natasha41575 | ||
| - KnVerey | ||
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| **Status**: implementable | ||
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| ## Summary | ||
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| The `kustomize localize` command creates a “localized” copy, of both the target kustomization and files target | ||
| references, in which the kustomization files contain, instead of remote references, local paths to their downloaded | ||
| locations. The command is part of an effort to enable `kustomize build` to run without network access. | ||
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| ## Motivation | ||
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| monopole originally proposed the command `kustomize localize` | ||
| in [this issue](https://github.com/kubernetes-sigs/kustomize/issues/3980). | ||
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| Users run `kustomize build` in many environments with limited network access. For example, CI/CD pipelines often only | ||
| have access to the internal network. Server-side applications like Config Sync are concerned with the security | ||
| vulnerabilities of git, which `kustomize build` uses to fetch remote files. | ||
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| These use cases would benefit from a kustomize solution that downloads all remote files that a `kustomize build` target | ||
| references, into a copy of target that references the downloaded files instead. Admins could upload the localized copy | ||
| to an internal repo so that pipelines and applications can run `kustomize build` on the copy without a network | ||
| dependency. | ||
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| The proposed command nearly achieves the solution by downloading all remote files directly referenced by the target or | ||
| by a recursively referenced kustomization file. The command also downloads remote exec binaries of referenced KRM | ||
| functions, which are the only potential source of remote files other than kustomizations. The only remote files that | ||
| this proposal does not cover and that `kustomize build` still needs to run are remote images and custom fields in KRM | ||
| functions. Downloaded images would live only in local caches and thus, are not worth localizing. Kustomize cannot | ||
| currently identify custom fields, though this may change with one of the proposed solutions | ||
| in [issue #4154](https://github.com/kubernetes-sigs/kustomize/issues/4154). | ||
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| The proposed command has the added benefit of increasing user confidence in the integrity of their kustomization builds. | ||
| Locally downloaded files, unlike urls, give users full control of file content. At the same time, the command does this | ||
| without modifying the original kustomization so that users can always run the command on the original again to fetch | ||
| upstream changes. | ||
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| **Goals:** | ||
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| 1. This command should localize | ||
| * all remote files that a kustomization file directly references | ||
| * remote exec binaries of referenced KRM functions | ||
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| This command achieves this goal if, in the absence of remote images and custom fields in KRM | ||
| functions, `kustomize build` can run on the localized copy without network access. | ||
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| **Non-goals:** | ||
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| 1. This command should not localize remote images or custom fields in KRM functions. | ||
| 2. This command should not copy files that the target kustomization does not reference. | ||
| 3. This command should not serve as a package manager. | ||
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| ## Proposal | ||
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| The command takes the following form: | ||
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| <pre> | ||
| <b>kustomize localize</b> <ins>target</ins> <ins>newDir</ins> [-s <ins>scope</ins>] [-n] | ||
| </pre> | ||
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| where the arguments are: | ||
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| * `target`: a directory with a top-level kustomization file that kustomize will localize; can be a path to a local | ||
| directory or a url to a remote directory | ||
| * `newDir`: optional destination directory of the localized copy of `target`; if not specified, the destination is a | ||
| directory named `localized-{target}` in the same directory as `scope` | ||
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| and the flags are: | ||
| * `-s`, `--scope` | ||
| `scope`: optional root directory, files outside which kustomize is not allowed to copy and localize; if not specified, | ||
| takes on value of `target` | ||
| * `-n`, `--no-verify`: do not verify that the outputs of `kustomize build` for `target` and `newDir` are the same after | ||
| localization | ||
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| The command creates a copy of the `target` kustomization and the local files that `target` references at `newDir`. We | ||
| define the "files that `target` references" as: | ||
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| * kustomization files that `target` directly or transitively references | ||
| * configuration files that referenced kustomization files reference | ||
| * exec binaries of referenced KRM functions | ||
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| Here, configuration file means a non-kustomization yaml file. The command cannot run on `target`s that need | ||
| the `--load-restrictor LoadRestrictionsNone` flag on `kustomize build`. The command only copies referenced files that | ||
| reside inside `scope`. | ||
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| The command localizes the copy of `target` at `newDir` by downloading all remote files that `target` | ||
| references. Users do not have executable permission for downloaded exec binaries that KRM functions reference and for | ||
| each such exec binary, the command will print a warning message to that effect. | ||
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| The command creates a new `localized-files` directory, next to the file that referenced the downloaded files, to hold | ||
| said files. Inside `localized-files`, the downloads are located on path: | ||
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| <pre> | ||
| <ins>domain</ins> / <ins>organization</ins> / <ins>repo</ins> / <ins>version</ins> / <ins>path/to/file/in/repo</ins> | ||
| </pre> | ||
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| where `version` corresponds to the `ref` query string parameter in the url, though ideally `version` ia a stable tag as | ||
| opposed to a branch. | ||
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| The command replaces remote references in `newDir` with the local paths of the downloaded files. To help ensure | ||
| that `newDir` is a clean copy, the command additionally overwrites absolute path references into `target` to point | ||
| to `newDir`. | ||
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| As a convenience to the user, in the absence of the `--no-verify` flag, the command automatically tries to | ||
| run `kustomize build`, without any flags, on `target` and the localized `newDir` to compare their outputs. The command | ||
| indicates success if the outputs match and throws an error with the diff summary otherwise. This check, however, is not | ||
| useful for certain `target`s, including those that need flags to build. In these cases, the command prints next steps | ||
| that users can follow to check the output themselves. For example, for `target`s that reference KRM functions with a | ||
| remote exec binary, the command suggests the user: | ||
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| 1. add executable permissions for the downloaded exec binaries in `newDir` **that the user trusts** | ||
| 2. run `kustomize build` with flags `--enable-alpha-plugins --enable-exec` and self-verify the outputs | ||
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| **Error cases**: | ||
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| * `target` does not have a top-level kustomization file | ||
| * `kustomize build` needs `--load-restrictor LoadRestrictionsNone` to run on `target` | ||
| * `newDir` already exists | ||
| * `scope` does not contain `target` | ||
| * `target` references a local path that traverses outside of `scope` | ||
| * remote reference does not have a `version` | ||
| * `localized-files` directory already exists | ||
| * kustomization file is malformed | ||
| * cycle of kustomization file references exists | ||
| * `kustomize build` produces different output for `target` and `newDir` in the absence of `--no-verify` | ||
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| Depending on feedback, we may add an `--overwrite` flag in the future to allow users to update an existing `newDir` by | ||
| running the command again. | ||
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| **Warning cases**: | ||
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| * KRM function references remote exec binary, in which case the downloaded exec binary is not executable | ||
| * KRM function has container image that the user might not have locally | ||
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| ### User Stories | ||
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| #### Story 1 | ||
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| My company’s CI/CD pipeline currently pulls an `example` directory from our internal package management site. I want the | ||
| CI/CD pipeline to additionally run `kustomize build example/overlay`. My setup looks like this: | ||
| ```shell | ||
| └── example | ||
| ├── overlay | ||
| │ └── kustomization.yaml | ||
| └── base | ||
| └── kustomization.yaml | ||
| ``` | ||
| ```shell | ||
| # example/overlay/kustomization.yaml | ||
| resources: | ||
| - ../base | ||
| - https://raw.githubusercontent.com/kubernetes-sigs/kustomize/v1.0.6/examples/helloWorld/deployment.yaml | ||
| ``` | ||
| ```shell | ||
| # example/base/kustomization.yaml | ||
| resources: | ||
| - github.com/kubernetes-sigs/kustomize/examples/multibases?ref=v1.0.6 | ||
| - https://raw.githubusercontent.com/kubernetes-sigs/kustomize/v1.0.6/examples/helloWorld/configMap.yaml | ||
| ``` | ||
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| I get an error from `kustomize build` in the pipeline because my configurations have remote references, but my CI/CD | ||
| pipeline does not have external network access. | ||
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| Fortunately, I remember that I can run `kustomize localize` on `example/overlay` on my local machine. I can then upload | ||
| the localized directory to my company’s internal package management site for the CI/CD pipeline to pull and build | ||
| instead. I run | ||
| `kustomize localize example/overlay -s example`, where my `target` is `example/overlay`, I accept the default location | ||
| and name of `newDir`, and I expand my `scope` to `example` because `example/overlay` references `example/base`. I get | ||
| the following output: | ||
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| ```shell | ||
| $ kustomize localize example/overlay -s example | ||
| SUCCESS: example/overlay, localized-overlay produce same kustomize build output | ||
| ``` | ||
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| ```shell | ||
| ├── example # old kustomization directory | ||
| │ ├── overlay | ||
| │ │ └── kustomization.yaml | ||
| │ └── base | ||
| │ └── kustomization.yaml | ||
| └── localized-overlay # the new, localized kustomization directory | ||
| ├── kustomization.yaml | ||
| ├── base | ||
| │ ├── kustomization.yaml | ||
| │ └── localized-files | ||
| │ └── github.com | ||
| │ └── kubernetes-sigs | ||
| │ └── kustomize | ||
| │ └── v1.0.6 | ||
| │ └── examples | ||
| │ ├── helloWorld | ||
| │ │ └── configMap.yaml | ||
| │ └── multibases | ||
| │ ├── base | ||
| │ │ └── pod.yaml | ||
| │ ├── dev | ||
| │ ├── kustomization.yaml | ||
| │ ├── production | ||
| │ └── staging | ||
| └── overlay | ||
| ├── kustomization.yaml | ||
| └── localized-files | ||
| └── github.com | ||
| └── kubernetes-sigs | ||
| └── kustomize | ||
| └── v1.0.6 | ||
| └── examples | ||
| └── helloWorld | ||
| └── deployment.yaml | ||
| ``` | ||
| ```shell | ||
| # localized-overlay/overlay/kustomization.yaml | ||
| resources: | ||
| - ../base | ||
| - ./localized-files/github.com/kubernetes-sigs/kustomize/examples/helloWorld/deployment.yaml | ||
| ``` | ||
| ```shell | ||
| # localized-overlay/base/kustomization.yaml | ||
| resources: | ||
| - ./localized-files/github.com/kubernetes-sigs/kustomize/examples/multibases | ||
| - ./localized-files/github.com/kubernetes-sigs/kustomize/examples/helloWorld/configMap.yaml | ||
| ``` | ||
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| Now, I upload `localized-overlay` from my local setup to my company’s internal package management site. I change the | ||
| commands in my CI/CD pipeline to pull `localized-overlay` before running `kustomize build localized-overlay`, and the | ||
| command executes successfully! | ||
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| ### Risks and Mitigations | ||
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| One could argue that while uploading the localized `newDir` to a repository, a user could accidentally leak Secrets that | ||
| were originally remote in a more private repo. This event is not very likely, as the servers that the user intends to | ||
| consume the localized kustomizations often only have access to internal, private networks and repos. Nonetheless, users | ||
| should have enough context in the case of Secrets to make the right decision. Users should have a basic understanding of | ||
| the files that their `target` kustomizations reference and of the files that they plan to upload to repos. Secret | ||
| configurations are also not too difficult to identify. | ||
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| Exec binaries that KRM functions reference are a different story. `kustomize localize` downloads remote exec binaries | ||
| that, if malicious, are capable of almost anything during subsequent `kustomize build` calls. The command mitigates this | ||
| risk by leaving these downloaded exec binaries without executable permissions and warning the user, as mentioned in | ||
| **Proposal**. `kustomize build` can only run the exec binary after the user deems the binary safe and changes its | ||
| permissions. | ||
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| Still another risk may be that if a user's kustomization tree is large, `kustomize localize` may be copying files from | ||
| unexpected locations. The command mitigates this risk with the `scope` flag. If not set, `kustomize localize` only | ||
| copies files in `target`. Otherwise, the user specifies `scope`and understands that `kustomize localize` only copies | ||
| files in `scope`. The qualification that the command can only localize `target`s that follow load restrictions helps | ||
| mitigate this risk as well. | ||
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| ### Dependencies | ||
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| N/A | ||
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| ### Scalability | ||
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| Large kustomization trees slows the performance of `kustomize localize`. These trees can have large local subtrees, have | ||
| large remote subtrees, be deeply nested, or be wide, with each overlay referencing multiple bases. Regardless of the | ||
| cause, large kustomization trees inevitably takes longer to copy and download. Parts of the kustomize code are not | ||
| thread-safe, which precludes parallel execution. | ||
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| On a separate note, a chain of remote kustomization directories in which the current kustomization file references the | ||
| next remote kustomization directories could create a `newDir` with deeply nested `localized-files`. This directory | ||
| structure would impede users’ navigation of `newDir`. However, this scenario should be unlikely as most kustomizations | ||
| only consist of a few layers. | ||
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| The creation of the `localized-files` directory local to the referencing kustomization file additionally prevents the | ||
| different layers of kustomization files from sharing the same copy of the remote files. Following the same logic, | ||
| different potential `target` directories cannot share copies either. | ||
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| ## Drawbacks | ||
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| Users whose layered kustomizations form a complex directory tree structure may have a hard time finding an | ||
| appropriate `scope`. However, many kustomizations exist in repositories, allowing the user to easily choose the repo | ||
| root as a valid `scope`. The warning messages that `kustomize localize` outputs for reference paths that extend | ||
| beyond `scope` should also help. | ||
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| ## Alternatives | ||
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| * Instead of downloading into `newDir`, `kustomize localize` could download all remote files into a directory specified | ||
| by some global environment variable (like in Golang), which would preclude deeply nested directories and allow | ||
| different kustomization files to share configurations. On top of that, if `kustomize build` had the added | ||
| functionality to check for previous downloads of remote references at said global location, `kustomize localize` would | ||
| not need to overwrite the remote references in `target` to the local downloads. As a result, `kustomize localize` | ||
| would need to neither write to `target` nor copy `target` into `newDir`. The user would not need to specify a `scope` | ||
| either. <br></br> | ||
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| Despite its advantages, the alternative design violates the self-contained nature of each kustomize layer. Users would | ||
| be unable to upload a fully localized kustomization directory in version control. Furthermore, this alternative | ||
| complicates the existing kustomize workflow by requiring the setup of global environment variables. | ||
| <br></br> | ||
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| * The command could, instead of making a copy, modify `target` directly. However, users would not have an easy way to | ||
| undo the command, which is undesirable. | ||
| <br></br> | ||
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| * Instead of requiring the user to specify a second argument `scope`, the command could by definition limit its copying | ||
| to `target`. However, in the case of **Story 1**, the command would force the user to set `target` to `example` in | ||
| order to include `example/base` in the localization of `example/overlay`. The user would then have to create a | ||
| kustomization file at `example` that points to `example/overlay` under the `resources` field. The creation of the | ||
| kustomization file solely for this purpose is messy and more work for the user. | ||
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| ## Rollout Plan | ||
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| This command will have at least alpha and GA releases. Depending on user feedback, we may add a beta. | ||
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| ### Alpha | ||
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| This release will not support | ||
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| * load restrictions check | ||
| * KRM functions | ||
| * absolute paths | ||
| * `target` kustomization with reference cycles | ||
| * any verification in the form of `--no-verification` flag or automatically running `kustomize build` at the end of | ||
| localization | ||
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| The entire command will be new in the alpha release, and so will not require an alpha flag. The command will not be | ||
| available in `kubectl kustomize` either as kubectl only has `kustomize build` builtin. | ||
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| ### Beta/GA | ||
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| This release should have all features documented in this proposal. Though, we may make changes based on user feedback. |