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3.6. Configuring swap space with cloud-init on Azure

3.6. Configuring swap space with cloud-init on Azure

To use swap space for a Red Hat Enterprise Linux (RHEL) virtual machine (VM) on Microsoft Azure, you need to create a swap partition on the ephemeral disk. Only use the ephemeral disk for creating a swap partition, not the operating system disk or data (storage) disk. Because the ephemeral disk is deleted when the virtual machine is deleted, the swap partition is also removed.

You can use the cloud-init utility to configure a swap partition on the ephemeral disk on-demand. Ephemeral disk is a local storage of the VM, while a resource disk is mounted storage on VM itself. Both storage types store data temporarily. Deleting, moving, stopping, or failure of the VM will result in the loss of the data stored on the ephemeral or resource disk.

重要

Do not use the ephemeral disk for persistent data. All contents, including the swap partition, are deleted when the VM is stopped or moved.

Prerequisites

You have installed the cloud-init utility on the VM.
You have disabled the swap configuration in the Windows Azure Linux Agent (WALA) by setting the parameters in the /etc/waagent.conf file:
```
ResourceDisk.Format=n
ResourceDisk.EnableSwap=n
ResourceDisk.SwapSizeMB=0
```
You have an ephemeral disk available on the VM.

Procedure

Log in to the VM.
Create and edit the /etc/cloud/cloud.cfg.d/00-azure-swap.cfg configuration file and add the following cloud-init configuration to the file:
```
# vi /etc/cloud/cloud.cfg.d/00-azure-swap.cfg
```
```
#cloud-config
disk_setup:
  ephemeral0:
    table_type: gpt
    layout: [66, [33,82]]
    overwrite: true
fs_setup:
  - device: ephemeral0.1
    filesystem: ext4
  - device: ephemeral0.2
    filesystem: swap
mounts:
  - ["ephemeral0.1", "/mnt"]
  - ["ephemeral0.2", "none", "swap", "sw,nofail,x-systemd.requires=cloud-init.service", "0", "0"]
```
This configuration:
- Partitions the ephemeral disk (ephemeral0) with a GPT partition table.
- Creates two partitions: 66% for a file system (mounted at /mnt) and 33% for swap space.
- Formats the first partition as ext4 and the second partition as swap.
- Configures automatic mounting of both partitions at boot time.
  注意
  The partition layout [66, [33,82]] allocates 66% of the disk to the first partition and 33% to the second partition. The 82 in the second partition specification indicates a Linux swap partition type. You can adjust these percentages based on your requirements.
Verify the configuration file for any errors:
```
# cloud-init devel schema --config-file /etc/cloud/cloud.cfg.d/00-azure-swap.cfg
```
If the configuration is valid, the command returns no errors.

Verification

After you reboot the VM, check that the swap partition is configured and active by verifying the active swap space, swap usage, and the swap partition entry in the /etc/fstab file.

Check active swap space:

$ swapon -s

The output should show the swap partition from ephemeral0.2:

Filename                 Type        Size      Used    Priority
/dev/ephemeral0.2     partition     8388604     0      -2

Check swap usage:

$ free -h

The output should show swap space in the Swap row:

         total        used        free      shared      buffered/cache   available
Mem:     7.8Gi        1.2Gi       5.8Gi        16MiB       800MiB       6.3Gi
Swap:    8.0Gi        0B          8.0Gi

Verify the swap partition is present in the /etc/fstab file:
```
$ grep swap /etc/fstab
```
The output should include an entry for the swap partition, for example:
```
/dev/ephemeral0.2   none     swap  sw,nofail,x-systemd.requires=cloud-init.service   0       0
```

3.6. Configuring swap space with cloud-init on Azure

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