Understanding and using the Azure Linux Agent
Azure has two different deployment models for creating and working with resources: Resource Manager and classic. This article covers using both models, but Microsoft recommends that most new deployments use the Resource Manager model.
The Microsoft Azure Linux Agent (waagent) manages Linux & FreeBSD provisioning, and VM interaction with the Azure Fabric Controller. It provides the following functionality for Linux and FreeBSD IaaS deployments:
See the Azure Linux agent README for additional details.
- Creation of a user account
- Configuring SSH authentication types
- Deployment of SSH public keys and key pairs
- Setting the host name
- Publishing the host name to the platform DNS
- Reporting SSH host key fingerprint to the platform
- Resource Disk Management
- Formatting and mounting the resource disk
- Configuring swap space
- Manages routes to improve compatibility with platform DHCP servers
- Ensures the stability of the network interface name
- Configures virtual NUMA (disable for kernel <2.6.37)
- Consumes Hyper-V entropy for /dev/random
- Configures SCSI timeouts for the root device (which could be remote)
- Console redirection to the serial port
- Detects and bootstraps the VMM agent for Linux when running in a System Center Virtual Machine Manager 2012 R2 environment
- Inject component authored by Microsoft and Partners into Linux VM (IaaS) to enable software and configuration automation
- VM Extension reference implementation on https://github.com/Azure/azure-linux-extensions
The information flow from the platform to the agent occurs via two channels:
- A boot-time attached DVD for IaaS deployments. This DVD includes an OVF-compliant configuration file that includes all provisioning information other than the actual SSH keypairs.
- A TCP endpoint exposing a REST API used to obtain deployment and topology configuration.
The following systems have been tested and are known to work with the Azure Linux Agent:
This list may differ from the official list of supported systems on the Microsoft Azure Platform, as described here: http://support.microsoft.com/kb/2805216
- CentOS 6.3+
- Red Hat Enterprise Linux 6.7+
- Debian 7.0+
- Ubuntu 12.04+
- openSUSE 12.3+
- SLES 11 SP3+
- Oracle Linux 6.4+
Other Supported Systems:
- FreeBSD 10+ (Azure Linux Agent v2.0.10+)
The Linux agent depends on some system packages in order to function properly:
- Python 2.6+
- OpenSSL 1.0+
- OpenSSH 5.3+
- Filesystem utilities: sfdisk, fdisk, mkfs, parted
- Password tools: chpasswd, sudo
- Text processing tools: sed, grep
- Network tools: ip-route
- Kernel support for mounting UDF filesystems.
Installation using an RPM or a DEB package from your distribution's package repository is the preferred method of installing and upgrading the Azure Linux Agent. All the endorsed distribution providers integrate the Azure Linux agent package into their images and repositories.
Refer to the documentation in the Azure Linux Agent repo on GitHub for advanced installation options, such as installing from source or to custom locations or prefixes.
Command Line Options
- verbose: Increase verbosity of specified command
- force: Skip interactive confirmation for some commands
- help: Lists the supported commands and flags.
deprovision: Attempt to clean the system and make it suitable for re-provisioning. This operation deleted the following:
- All SSH host keys (if Provisioning.RegenerateSshHostKeyPair is 'y' in the configuration file)
- Nameserver configuration in /etc/resolv.conf
- Root password from /etc/shadow (if Provisioning.DeleteRootPassword is 'y' in the configuration file)
- Cached DHCP client leases
- Resets host name to localhost.localdomain
Deprovisioning does not guarantee that the image is cleared of all sensitive information and suitable for redistribution.
- deprovision+user: Performs everything under -deprovision (above) and also deletes the last provisioned user account (obtained from /var/lib/waagent) and associated data. This parameter is when de-provisioning an image that was previously provisioning on Azure so it may be captured and re-used.
- version: Displays the version of waagent
- serialconsole: Configures GRUB to mark ttyS0 (the first serial port) as the boot console. This ensures that kernel bootup logs are sent to the serial port and made available for debugging.
- daemon: Run waagent as a daemon to manage interaction with the platform. This argument is specified to waagent in the waagent init script.
- start: Run waagent as a background process
A configuration file (/etc/waagent.conf) controls the actions of waagent. A sample configuration file is shown below:
Provisioning.Enabled=y Provisioning.DeleteRootPassword=n Provisioning.RegenerateSshHostKeyPair=y Provisioning.SshHostKeyPairType=rsa Provisioning.MonitorHostName=y Provisioning.DecodeCustomData=n Provisioning.ExecuteCustomData=n Provisioning.AllowResetSysUser=n Provisioning.PasswordCryptId=6 Provisioning.PasswordCryptSaltLength=10 ResourceDisk.Format=y ResourceDisk.Filesystem=ext4 ResourceDisk.MountPoint=/mnt/resource ResourceDisk.MountOptions=None ResourceDisk.EnableSwap=n ResourceDisk.SwapSizeMB=0 LBProbeResponder=y Logs.Verbose=n OS.RootDeviceScsiTimeout=300 OS.OpensslPath=None HttpProxy.Host=None HttpProxy.Port=None AutoUpdate.Enabled=y
The various configuration options are described in detail below. Configuration options are of three types; Boolean, String or Integer. The Boolean configuration options can be specified as "y" or "n". The special keyword "None" may be used for some string type configuration entries as detailed below.
This allows the user to enable or disable the provisioning functionality in the agent. Valid values are "y" or "n". If provisioning is disabled, SSH host and user keys in the image are preserved and any configuration specified in the Azure provisioning API is ignored.
Provisioning.Enabled parameter defaults to "n" on Ubuntu Cloud Images that use cloud-init for provisioning.
If set, the root password in the /etc/shadow file is erased during the provisioning process.
If set, all SSH host key pairs (ecdsa, dsa and rsa) are deleted during the provisioning process from /etc/ssh/. And a single fresh key pair is generated.
The encryption type for the fresh key pair is configurable by the Provisioning.SshHostKeyPairType entry. Please note that some distributions will re-create SSH key pairs for any missing encryption types when the SSH daemon is restarted (for example, upon a reboot).
This can be set to an encryption algorithm type that is supported by the SSH daemon on the virtual machine. The typically supported values are "rsa", "dsa" and "ecdsa". Note that "putty.exe" on Windows does not support "ecdsa". So, if you intend to use putty.exe on Windows to connect to a Linux deployment, please use "rsa" or "dsa".
If set, waagent will monitor the Linux virtual machine for hostname changes (as returned by the "hostname" command) and automatically update the networking configuration in the image to reflect the change. In order to push the name change to the DNS servers, networking will be restarted in the virtual machine. This will result in brief loss of Internet connectivity.
If set, waagent will decode CustomData from Base64.
If set, waagent will execute CustomData after provisioning.
Provisioning.AllowResetSysUser Type: Boolean Default: n
This option allows the password for the sys user to be reset; default is disabled.
Algorithm used by crypt when generating password hash.
1 - MD5
2a - Blowfish
5 - SHA-256
6 - SHA-512
Length of random salt used when generating password hash.
If set, the resource disk provided by the platform will be formatted and mounted by waagent if the filesystem type requested by the user in "ResourceDisk.Filesystem" is anything other than "ntfs". A single partition of type Linux (83) will be made available on the disk. Note that this partition will not be formatted if it can be successfully mounted.
This specifies the filesystem type for the resource disk. Supported values vary by Linux distribution. If the string is X, then mkfs.X should be present on the Linux image. SLES 11 images should typically use 'ext3'. FreeBSD images should use 'ufs2' here.
This specifies the path at which the resource disk is mounted. Note that the resource disk is a temporary disk, and might be emptied when the VM is deprovisioned.
Specifies disk mount options to be passed to the mount -o command. This is a comma separated list of values, ex. 'nodev,nosuid'. See mount(8) for details.
If set, a swap file (/swapfile) is created on the resource disk and added to the system swap space.
The size of the swap file in megabytes.
If set, log verbosity is boosted. Waagent logs to /var/log/waagent.log and leverages the system logrotate functionality to rotate logs.
If set, the agent will attempt to install and then load an RDMA kernel driver that matches the version of the firmware on the underlying hardware.
This configures the SCSI timeout in seconds on the OS disk and data drives. If not set, the system defaults are used.
This can be used to specify an alternate path for the openssl binary to use for cryptographic operations.
If set, the agent will use this proxy server to access the internet.
AutoUpdate.Enabled Type: Boolean Default: y
Enable or disable auto-update for goal state processing; default is enabled.
Ubuntu Cloud Images
Note that Ubuntu Cloud Images utilize cloud-init to perform many configuration tasks that would otherwise be managed by the Azure Linux Agent. Please note the following differences:
- Provisioning.Enabled defaults to "n" on Ubuntu Cloud Images that use cloud-init to perform provisioning tasks.
The following configuration parameters have no effect on Ubuntu Cloud Images that use cloud-init to manage the resource disk and swap space:
Please see the following resources to configure the resource disk mount point and swap space on Ubuntu Cloud Images during provisioning: