Kubectl Plugins¶

I must admit - I love tools that can be extended beyond what was initially intended for said tool. The kubectl command is such a great example of this!

Extending kubectl has been possible for some time and the mechanism is rather straight forward. In time, however, it was expected that there will be a number of useful extensions/plugins that many more people would want to use. The challange is that kubectl itself never intended to also manage all these extra functionality - it's beyond the scope of it's maintainers and it was up to the community of users to solve this problem.

Enter krew, which "... helps you discover plugins, install and manage them on your machine.".

The installation instructions is pretty straight forward and worked without any issues on my Ubuntu system.

After installation, make sure your local index is up to date:

kubectl krew update

It's very similar to apt or brew or other package managers you may be familiar with.

Usage Example - Something Familiar¶

A while back, I demonstrated a REST API solution that would provide useful resource capacity information. In that blog post, I showed how you could use curl to obtain the data on the command line.

So for this very quick intro to krew, I'm going to solve the same problem, but with a kubectl plugin that uses information already available through the standard Kubernetes API: kube-capacity

There are several ways to search for plugins, for example the command kubectl krew search resource may yield the following results:

NAME               DESCRIPTION                                         INSTALLED
resource-capacity  Provides an overview of resource requests, limi...  no
resource-snapshot  Prints a snapshot of nodes, pods and HPAs resou...  no
resource-versions  Print supported API resource versions               no

To install resource-capacity is as easy as running the following command:

kubectl krew install resource-capacity

The output from the command is just as helpful:

Updated the local copy of plugin index.
Installing plugin: resource-capacity
Installed plugin: resource-capacity
\
 | Use this plugin:
 |      kubectl resource-capacity
 | Documentation:
 |      https://github.com/robscott/kube-capacity
/
WARNING: You installed plugin "resource-capacity" from the krew-index plugin repository.
   These plugins are not audited for security by the Krew maintainers.
   Run them at your own risk.

And a quick run of the command kubectl resource-capacity immediately yields some useful results:

NODE    CPU REQUESTS   CPU LIMITS    MEMORY REQUESTS   MEMORY LIMITS
*       1950m (32%)    3500m (58%)   1158Mi (4%)       2218Mi (9%)
node1   700m (35%)     1000m (50%)   396Mi (4%)        682Mi (8%)
node2   500m (25%)     1000m (50%)   256Mi (3%)        512Mi (6%)
node3   750m (37%)     1500m (75%)   506Mi (6%)        1024Mi (12%)

Compare that with the JSON output from the pykles REST service as describe in the earlier blog post:

{
    "Nodes": [
        {
            "NodeName": "node1",
            "CPU": {
                "Capacity": 2000,
                "Allocatable": 2000,
                "Requests": {
                    "InstrumentedValue": 500.0,
                    "Percent": 25.0
                },
                "Limits": {
                    "InstrumentedValue": 1000.0,
                    "Percent": 50.0
                }
            },
            "RAM": {
                "Capacity": 8344223744,
                "Allocatable": 8344223744,
                "Requests": {
                    "InstrumentedValue": 341835776.0,
                    "Percent": 4.096675574475104
                },
                "Limits": {
                    "InstrumentedValue": 715128832.0,
                    "Percent": 8.570345833717855
                }
            }
        },
        {
            "NodeName": "node2",
            "CPU": {
                "Capacity": 2000,
                "Allocatable": 2000,
                "Requests": {
                    "InstrumentedValue": 500.0,
                    "Percent": 25.0
                },
                "Limits": {
                    "InstrumentedValue": 1000.0,
                    "Percent": 50.0
                }
            },
            "RAM": {
                "Capacity": 8344223744,
                "Allocatable": 8344223744,
                "Requests": {
                    "InstrumentedValue": 268435456.0,
                    "Percent": 3.2170213100172598
                },
                "Limits": {
                    "InstrumentedValue": 536870912.0,
                    "Percent": 6.4340426200345195
                }
            }
        },
        {
            "NodeName": "node3",
            "CPU": {
                "Capacity": 2000,
                "Allocatable": 2000,
                "Requests": {
                    "InstrumentedValue": 750.0,
                    "Percent": 37.5
                },
                "Limits": {
                    "InstrumentedValue": 1500.0,
                    "Percent": 75.0
                }
            },
            "RAM": {
                "Capacity": 8344231936,
                "Allocatable": 8344231936,
                "Requests": {
                    "InstrumentedValue": 530579456.0,
                    "Percent": 6.358637440444224
                },
                "Limits": {
                    "InstrumentedValue": 1073741824.0,
                    "Percent": 12.868072606748788
                }
            }
        }
    ]
}

It's the same output, but only one is really useful for human consumption!

Tags¶

kubernetes, cli