Proposal for new command "kustomize localize"

proposals/22-04-localize-command.md

@@ -35,14 +35,20 @@ The proposed command nearly achieves the solution by downloading all remote file
 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 kustomize cannot know the form that custom fields will
-take. Thus, neither is worth localizing.
+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).
+
+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.
 
 **Goals:**
 
-1. This command should localize 
-   * all remote files that a kustomization file directly references 
-   * remote exec binaries of referenced KRM functions 
+1. This command should localize
+   * all remote files that a kustomization file directly references
+   * remote exec binaries of referenced KRM functions
 
    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.
@@ -58,16 +64,22 @@ take. Thus, neither is worth localizing.
 The command takes the following form:
 
 <pre>
-<b>kustomize localize</b> <ins>target</ins> <ins>scope</ins> <ins>newDir</ins>
+<b>kustomize localize</b> <ins>target</ins> <ins>newDir</ins> [-s <ins>scope</ins>] [-n]
 </pre>
 
 where the arguments are:
 
 * `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
-* `scope`: optional root directory, files outside which kustomize is not allowed to copy and localize; if not specified,
+* `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`
+
+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`
-* `newDir`: destination directory of the localized copy of `target`
+* `-n`, `--no-verify`: do not verify that the outputs of `kustomize build` for `target` and `newDir` are the same after
+  localization
 
 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:
@@ -76,59 +88,79 @@ define the "files that `target` references" as:
 * configuration files that referenced kustomization files reference
 * exec binaries of referenced KRM functions
 
-Here, configuration file means a non-kustomization yaml file. The command only copies referenced files that reside
-inside `scope`.
+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`.
 
-The command localizes the copy of `target` at `newDir` by downloading all remote files that `target` references. The
-downloaded files placed in a new `localized-files` directory next to the file that referenced the downloaded files.
-Inside `localized-files`, the downloads are located on path:
+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. 
+
+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:
 
 <pre>
-<ins>remote-host</ins> / <ins>organization</ins> / <ins>repo</ins> / <ins>version</ins> / <ins>path-to-file-in-repo</ins>
+<ins>domain</ins> / <ins>organization</ins> / <ins>repo</ins> / <ins>version</ins> / <ins>path/to/file/in/repo</ins>
 </pre>
 
-The command rewrites remote references in `newDir` to the local paths of the downloaded files. To help ensure
+where `version` corresponds to the `ref` query string parameter in the url, though ideally `version` ia a stable tag as
+opposed to a branch.
+
+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`.
 
+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:
+
+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
+
 **Error cases**:
+
 * `target` does not have a top-level kustomization file
-* `scope` does not contain `target`
+* `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
-* remote reference does not have a version
 * 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`
 
-**Warning cases**:
-* `target` references a local path that traverses outside of `scope`
-* KRM function has container image that the user might not have locally
+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.
 
-For the warning cases, the command will ignore the reference and continue execution.
+**Warning cases**:
 
-If the command runs without any errors or warnings, `kustomize build` without `--load-restrictor LoadRestrictionsNone`
-on `target` and `newDir` should produce the same output.
+* 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
 
 ### User Stories
 
 #### Story 1
 
 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
@@ -141,144 +173,104 @@ pipeline does not have external network access.
 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 example/localized-overlay`, but I get the following warning:
-
-```
-$ kustomize localize example/overlay example/localized-overlay
-Warning: File example/overlay/kustomization.yaml refers to ../base on line 2. This reference is outside of scope: 
-         example/overlay. kustomize localize will skip this path.
-```
-
-because I forgot that `kustomize localize` can only process local references to files within
-`scope`. Therefore, the command could not copy `example/base` to `example/localized-overlay`or localize the remote
-references in `example/base`. The resulting file structure is as follows:
+`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:
 
+```shell
+$ kustomize localize example/overlay -s example
+SUCCESS: example/overlay, localized-overlay produce same kustomize build output
 ```
-└── example
-    ├── overlay
-    │   └── kustomization.yaml
-    ├── localized-overlay
-    │   ├── kustomization.yaml
-    │   └── localized-files
-    │       └── github.com
-    │           └── kubernetes-sigs
-    │               └── kustomize
-    │                   └── v1.0.6
-    │                       └── examples
-    │                           └── helloWorld
-    │                               └── deployment.yaml
-    └── base
-        └── kustomization.yaml
-```
-
-`kustomize build example/localized-overlay` will still run correctly outside the CI/CD pipeline because I chose to
-place `example/localized-overlay` in the same directory as `example/overlay`. As a result, relative paths,
-namely `../base`, in `example/localized-overlay` will point to the same files as their counterparts in `example/overlay`
-. However, `kustomize build example/localized-overlay` will still require network access to run.
 
-#### Story 2
-
-I am back again from **Story 1**, but this time ready to localize `base` too, instead of just the `overlay` directory.
-To localize both, I set my `scope` argument to `example` to make a copy of both directories. My setup still looks like
-that at the end of **Story 1**:
-
-```
-└── example
-    ├── overlay
-    │   └── kustomization.yaml
-    ├── localized-overlay
+```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
-    │                               └── deployment.yaml
-    └── base
-        └── kustomization.yaml
-```
-
-After I run `kustomize localize example/overlay example new-space/localized-example`, I get the
-following:
-
-```
-├── example                         # old kustomization directory
-│   ├── overlay
-│   │   └── kustomization.yaml
-│   ├── localized-overlay
-│   │   ├── kustomization.yaml
-│   │   └── localized-files
-│   │       └── github.com
-│   │           └── kubernetes-sigs
-│   │               └── kustomize
-│   │                   └── v1.0.6
-│   │                       └── examples
-│   │                           └── helloWorld
-│   │                               └── deployment.yaml
-│   └── base
-│       └── kustomization.yaml
-└── new-space
-    └── localized-example            # the new, localized kustomization directory
+    │                           ├── helloWorld
+    │                           │   └── configMap.yaml
+    │                           └── multibases
+    │                               ├── base
+    │                               │   └── pod.yaml
+    │                               ├── dev
+    │                               ├── kustomization.yaml
+    │                               ├── production
+    │                               └── staging
+    └── overlay
         ├── 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
+        └── localized-files
+            └── github.com
+                └── kubernetes-sigs
+                    └── kustomize
+                        └── v1.0.6
+                            └── examples
+                                └── helloWorld
+                                    └── deployment.yaml
 ```
-```
-# new-space/localized-example/overlay/kustomization.yaml
+```shell
+# localized-overlay/overlay/kustomization.yaml
 resources:
   - ../base
   - ./localized-files/github.com/kubernetes-sigs/kustomize/examples/helloWorld/deployment.yaml
 ```
-```
-# new-space/localized-example/base/kustomization.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
 ```
 
-Now, I upload `new-space/localized-example` from my local setup to my company’s internal package management site. I
-change the commands in my CI/CD pipeline to pull `localized-example` before running `kustomize build localized-example`,
-and the command executes successfully!
+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!
 
 ### Risks and Mitigations
-N/A
+
+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.
+
+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.
+
+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.
 
 ### Dependencies
+
 N/A
 
 ### Scalability
 
-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.
+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.
+
+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.
 
 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,
@@ -322,10 +314,14 @@ This command will have at least alpha and GA releases. Depending on user feedbac
 
 ### Alpha
 
-This release will ignore 
+This release will not support
 
-* local kustomization files that `target` references
+* 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
 
 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.