Add Persistent Storage

MonkOS is capable of creating and maintaining persistent volumes in your cloud environment. For example, you can create a volume usable by all containers in its region. This guide shows how to provision and mount such volume.

Persistent volumes are created close to the workloads, meaning that they will end up in the same region as the MonkOS node running the runnable or group in which the volume was specified.

Prerequisites

You need a MonkOS cluster with at least two nodes running in your chosen cloud to be able to try this out.

Step 1: Preparing the Kit

We will write a simple mongodb Kit to illustrate how the database could be stored on a persistent volume.

Basic Kit

database.yaml
namespace: guides

database:
  defines: runnable
  containers:
    mongodb:
      image: mongo
      image-tag: latest

Now add volume and mount definitions to the Kit:

database.yaml
namespace: guides

database:
  defines: runnable
  containers:
    mongodb:
      image: mongo
      image-tag: latest
      mounted-volumes:
        important-data:
          path: /data/db
  volumes:
    important-data:
      kind: local

It is perfectly fine to run with:

monk load database.yaml
monk run guides/database

The MongoDB database will use its local volume to store the data. This means that the data will be stored on the disk of the instance that is running this Kit.

In mounted-volumes for a container we chose to mount the volume in /data/db because that's the default path where MongoDB stores its data in mongo image. You can also add optional subdir property to mount the subdirectory of the referenced volume instead of root.

On host side, meaning that the instance with runnable and volume attached, the volume will be mounted in MonkOS volumes directory, you can change it by setting path for a volume.

database.yaml
...
database:
  defines: runnable
  containers:
    mongodb:
      image: mongo
      image-tag: latest
      mounted-volumes:
        important-data:
          path: /data/db
          subdir: data
volumes:
  important-data:
    kind: local
    path: <- `${monk-volume-path}/mongodb`

This will mount the volume in /root/.monk/volumes/mongodb/data on the host to /data/db in the container.

Extend Kit with Cloud Volume

Let's extend database.yaml with a cloud volume definition:

database.yaml
namespace: guides

database:
  defines: runnable
  containers:
    mongodb:
      image: mongo
      image-tag: latest
      mounted-volumes:
        important-data:
          path: /data/db
  volumes:
    important-data:
      kind: SSD
      size: 60
      name: mongodb-volume

We've added size and changed kind for our volume. The size is expressed in Gigabytes so our new volume will have 60GB. The kind is SSD - you can pick between HDD or SSD depending on your needs, some cloud providers have more volume types.

We've also added name for our volume. This is the name that will be used to create the volume in the cloud. If you do not specify a name, MonkOS will use the same name as volume reference (here important-data).

Step 2: Running the Kit

database.yaml
namespace: guides

database:
  defines: runnable
  containers:
    mongodb:
      image: mongo
      image-tag: latest
      mounted-volumes:
        important-data:
          path: /data/db
  volumes:
    important-data:
      kind: SSD
      size: 10
      name: mongodb-volume

Save this file as database.yaml and run with:

monk load database.yaml
monk run guides/database

Pick a tag that will place the workload in some cloud environment (this will not work when running locally).

The output should look similar to:

? Select tag to run on: sometag
✔ Starting the job... DONE
✔ Preparing nodes DONE
✔ Checking/pulling images DONE
✔ Started guides/database
✨ All done!
🔩 guides/database
└─🧊 Peer QmPVzBzu94DgqrKp2uQGZLyXaC9zoYpDL3idXs24b8R6vU
    └─📦 templates-local-guides-database-database
    ├─🧩 mongo:latest
    ├─💾 /root/.monk/volumes/mongodb -> /data/db
    └─🔌 open 174.138.39.138:27017 -> 27017
💡 You can inspect and manage your above stack with these commands:
    monk logs (-f) guides/database - Inspect logs
    monk shell     guides/database - Connect to the container's shell
    monk do        guides/database/action_name - Run defined action (if exists)
💡 Check monk help for more!

Step 3: Confirming the data was written to the volume

To confirm that the right volume was mounted:

monk shell guides/database

This will open a shell in the database container. Check if the mountpoint exists:

df -h

Filesystem      Size  Used Avail Use% Mounted on
overlay          25G  1.8G   23G   8% /
tmpfs            64M     0   64M   0% /dev
tmpfs           497M     0  497M   0% /sys/fs/cgroup
/dev/sda        9.8G  337M  9.0G   4% /data/db          <--- our volume
/dev/vda1        25G  1.8G   23G   8% /data/configdb
shm              64M     0   64M   0% /dev/shm
tmpfs           497M     0  497M   0% /proc/acpi
tmpfs           497M     0  497M   0% /proc/scsi
tmpfs           497M     0  497M   0% /sys/firmware

There should be some files present there already, check with:

ls /data/db

WiredTiger     _mdb_catalog.wt             index-1-641850887836602971.wt  lost+found
WiredTiger.lock    collection-0-641850887836602971.wt  index-3-641850887836602971.wt  mongod.lock
WiredTiger.turtle  collection-2-641850887836602971.wt  index-5-641850887836602971.wt  sizeStorer.wt
WiredTiger.wt      collection-4-641850887836602971.wt  index-6-641850887836602971.wt  storage.bson
WiredTigerHS.wt    diagnostic.data             journal

If you see similar output, it means that the cloud provided volume is mounted to the container ans stores the database.

Volume backups

MonkOS can back up any defined cloud volume using volume snapshots. To enable backups at any point you can add the following definition inside your volume (here important-data):

backup:
    rotation-days: 10
    every: 1
    kind: week
    start-time: 00:00
    start-day: MONDAY

This can be read as follows: At all times keep backups from last 10 days making a backup every week at midnight on Monday.

Times must be in HH:MM format, weekdays are one of MONDAY, TUESDAY, WEDNESDAY, THURSDAY, FRIDAY, SATURDAY, SUNDAY. The field kind sets the interval and can be one of day, hour, week.

MonkOS delegates the backup process to the cloud it's running on and the backups can be managed via the cloud console and won't disappear even if MonkOS fails or gets removed from your cloud account.

Full example of volumes with backup's usage

namespace: /postgres
postgres:
  defines: runnable
  containers:
    postgres:
      image: bitnami/postgresql
      mounted-volumes:
        postgres:
          path: /var/lib/postgresql/data
          subdir: data
  volumes:
    postgres:
      size: 2
      kind: HDD
      backup:
        rotation-days: 10
        every: 1
        kind: hour
        start-time: 00:00
        start-day: MONDAY

Conclusion

You are now running a MongoDB database which stores its data on a persistent volume. In case the workload fails or the instance running the database container ceases to exist your database contents will be safe on the persistent volume. This mechanism can be applied to any workload or group of workloads with one or many separate volumes.

Prerequisites​

Step 1: Preparing the Kit​

Basic Kit​

Extend Kit with Cloud Volume​

Step 2: Running the Kit​

Step 3: Confirming the data was written to the volume​

Volume backups​

Full example of volumes with backup's usage​

Conclusion​