Add proposal document for `helm export` and `helm import`

https://github.com/kubernetes/helm/issues/3309

PROPOSAL.md

@@ -0,0 +1,75 @@
+# Export and import feature proposal
+
+Export - ability to save currently installed releases into a single file (`helm export` command). Import - ability to restore (re-install)
+previously exported releases (`helm import` command).
+
+## Use cases
+
+### Disaster recovery
+
+A Cluster Administrator can run `helm export` command continuously or after releasing software. This command will save all Helm releases into a file.
+It will include all data associated with the release including name, version, chart, values and release history. This file can be uploaded to S3 bucket where it
+will be stored permanently. Later, in case of emergency, this file can be used to restore cluster state by running `helm import` command.
+
+### Creating new environment
+
+Typically, organizations run multiple environments. Example: DEV, STAGE, PROD. This can be achieved by either using a dedicated namespace in the single
+Kubernetes cluster or by creating a dedicated Kubernetes cluster for every environment. In either case, `helm export` and `helm import` can be used for creating
+new environments from scratch. `helm export` will save a snapshot of the environment and `helm import` will restore this snapshot in given Kubernetes cluster or namespace.
+
+## Implementation
+
+The following commands will be added to `helm` binary:
+
+* `helm export`
+* `helm import`
+
+The following actions will be added to tiller's `ReleaseServer`:
+
+* `func (s *ReleaseServer) Export(...)`
+* `func (s *ReleaseServer) Import(...)`
+
+### Export file format
+
+```protobuf
+syntax = "proto3";
+
+package hapi.export;
+
+message Metadata {
+  google.protobuf.Timestamp created_at = 1; // Timestamp when export file was created
+  string tiller_version = 2; // Version of tiller which was used
+}
+
+message Export {
+  hapi.export.Metadata metadata = 1; // Export file metadata
+  repeated hapi.release.Release releases = 2; // List of releases
+}
+```
+
+The protobuf representation of `hapi.export.Export` will be additionally gzipped.
+
+### helm export
+
+`helm export` will send a new gRPC request to `tiller` asking to create a new export file. `tiller` will prepare and send this file back to the client.
+All releases including the ones which were superseded by new versions will be saved.
+
+Arguments:
+
+* `--namespace` - Namespace to export. Defaults to the current kube config namespace.
+* `--file` - Output file path. Defaults to "helm-releases-<timestamp>.gz".
+
+### helm import
+
+`helm import` will send the passed export file to `tiller` and tiller will install all releases from this file in the given namespace.
+
+Arguments:
+
+* `--file` (Mandatory) - Path to the export file
+* `--namespace` - Namespace where tiller will re-install releases. Defaults to the current kube config namespace.
+* `--no-hooks` - Skip hooks
+* `--replace` - By default, helm will raise an error if any of the releases in the export file are already installed. This option will force tiller to replace them.
+
+## Alternatives
+
+* https://github.com/heptio/ark