---
title: " Running MongoDB on Kubernetes with StatefulSets "
date: 2017-01-30
slug: running-mongodb-on-kubernetes-with-statefulsets
url: /blog/2017/01/Running-Mongodb-On-Kubernetes-With-Statefulsets
author: >
  Sandeep Dinesh (Google Cloud Platform)
---

{{% warning %}}
This post is several years old. The code examples need changes to work on a current Kubernetes cluster.
{{% /warning %}}

Conventional wisdom says you can’t run a database in a container. “Containers are stateless!” they say, and “databases are pointless without state!”

Of course, this is not true at all. At Google, everything runs in a container, including databases. You just need the right tools. [Kubernetes 1.5](https://kubernetes.io/blog/2016/12/kubernetes-1-5-supporting-production-workloads/) includes the new [StatefulSet](/docs/concepts/abstractions/controllers/statefulsets/) API object (in previous versions, StatefulSet was known as PetSet). With StatefulSets, Kubernetes makes it much easier to run stateful workloads such as databases.

If you’ve followed my previous posts, you know how to create a [MEAN Stack app with Docker](http://blog.sandeepdinesh.com/2015/07/running-mean-web-application-in-docker.html), then [migrate it to Kubernetes](https://medium.com/google-cloud/running-a-mean-stack-on-google-cloud-platform-with-kubernetes-149ca81c2b5d) to provide easier management and reliability, and [create a MongoDB replica set](https://medium.com/google-cloud/mongodb-replica-sets-with-kubernetes-d96606bd9474) to provide redundancy and high availability.

While the replica set in my previous blog post worked, there were some annoying steps that you needed to follow. You had to manually create a disk, a ReplicationController, and a service for each replica. Scaling the set up and down meant managing all of these resources manually, which is an opportunity for error, and would put your stateful application at risk In the previous example, we created a Makefile to ease the management of these resources, but it would have been great if Kubernetes could just take care of all of this for us.

With StatefulSets, these headaches finally go away. You can create and manage your MongoDB replica set natively in Kubernetes, without the need for scripts and Makefiles. Let’s take a look how.

_Note: StatefulSets are currently a beta resource. The [sidecar container](https://github.com/cvallance/mongo-k8s-sidecar) used for auto-configuration is also unsupported._

**Prerequisites and Setup**

Before we get started, you’ll need a Kubernetes 1.5+ and the [Kubernetes command line tool](/docs/user-guide/prereqs/). If you want to follow along with this tutorial and use Google Cloud Platform, you also need the [Google Cloud SDK](http://cloud.google.com/sdk).

Once you have a [Google Cloud project created](https://console.cloud.google.com/projectcreate) and have your Google Cloud SDK setup (hint: gcloud init), we can create our cluster.

To create a Kubernetes 1.5 cluster, run the following command:

```
gcloud container clusters create "test-cluster"
 ```

This will make a three node Kubernetes cluster. Feel free to [customize the command](https://cloud.google.com/sdk/gcloud/reference/container/clusters/create) as you see fit.

Then, authenticate into the cluster:

```
gcloud container clusters get-credentials test-cluster
 ```

**Setting up the MongoDB replica set**

To set up the MongoDB replica set, you need three things: A [StorageClass](/docs/user-guide/persistent-volumes/#storageclasses), a [Headless Service](/docs/user-guide/services/#headless-services), and a [StatefulSet](/docs/concepts/abstractions/controllers/statefulsets/).

I’ve created the configuration files for these already, and you can clone the example from GitHub:

```
git clone https://github.com/thesandlord/mongo-k8s-sidecar.git

cd /mongo-k8s-sidecar/example/StatefulSet/
 ```

To create the MongoDB replica set, run these two commands:

```
kubectl apply -f googlecloud\_ssd.yaml

kubectl apply -f mongo-statefulset.yaml