Dual Mode Service Catalog CLI

Dual Mode Service Catalog CLI.md

Dual Mode Service Catalog CLI

We can use the same binary as a standalone Service Catalog CLI, and as a kubectl plugin, with only minor modifications.

Standalone Binary

This is what you see today with svcat.

Installation

curl -sLO https://servicecatalogcli.blob.core.windows.net/cli/latest/$(uname -s)/$(uname -m)/svcat
chmod +x ./svcat
mv ./svcat /usr/local/bin/

Upgrade

Performs an in-place upgrade of the binary.

svcat upgrade

This is on our backlog, currently upgrading involves repeating the installation steps.

Commands

$ svcat get bindings
$ svcat sync broker osba
$ svcat unbind mysql

Plugin

By adding a new svcat install-plugin command, we can use the binary in either standalone or plugin mode.

Flags passed to the plugin are intercepted by kubectl and are converted to environment variables:

• The flag must be defined in the manifest.
• Global kubectl flags, like --namespace, are converted to KUBECTL_PLUGINS_GLOBAL_FLAG_NAMESPACE.
• Command-specific flags, like svcat provision --class, are converted to KUBECTL_PLUGINS_LOCAL_FLAG_CLASS.

Installation

This will install the the svcat binary and an accompanying plugin manifest to ~/.kube/plugins/svcat/.

curl -sLo /tmp/svcat https://servicecatalogcli.blob.core.windows.net/cli/latest/$(uname -s)/$(uname -m)/svcat
chmod +x /tmp/svcat
/tmp/svcat install-plugin

Upgrade

Performs an in-place upgrade of the binary and the plugin manifest.

kubectl plugin svcat upgrade

Commands

In an ideal world, the plugin sub-command would not be necessary. When a sub-command is used that isn't a built-in command, kubectl would search for a matching plugin, making a command like kubectl svcat get bindings possible. We would need to follow-up to know if that was considered and rejected previously.

$ kubectl plugin svcat get bindings
$ kubectl plugin svcat sync broker osba
$ kubectl plugin svcat unbind mysql

Some commands are simple enough that you could use kubectl entirely, without using the plugin:

• kubectl plugin svcat bind mysql -> kubectl create -f mybinding.yaml
• kubectl plugin svcat unbind mysql-binding-1 -> kubectl delete servicebinding mysql-binding-1

Falling back to kubectl to perform easy tasks depart from the "domain-specific tool" goal of svcatt to use the same terms when speaking about service catalog on the command line. Rolling up multi-step concerns and tasks into a single domain-based task. For example svcat unbind mysql-instance, iterates all of the existing bindings and removes them. Yes, you can do the same with kubectl, but this fits an entire concept into a single command. It shouldn't be up to the user to know about these special cases.