installer

installer

The installer will install an OS on a machine using a Dominator image.

The installer is a command-line tool that will configure the network, fetch configuration data, format storage devices, install an OS image and then fast reboot into the newly installed OS. It is usually packaged into an installer image which may be network booted (via a PXE DHCP/TFTP server) or on portable storage media such as a USB flash drive or a CD-ROM containg an ISO-format image. Some machines have a BMC (Baseboard Management Controller) which supports network mounting a remote ISO image and booting from that.

The installer image is recommended to be small so that it may be loaded quickly. A common pattern is have only a kernel, modules, a busybox-based shell, some device discovery boot scripts and the installer binary.

The installer will scan the storage devices for a previously installed OS. If present, it will copy files from the old OS into a temporary object cache, computing checksums of the files. It uses this cache to skip downloading objects from the imageserver, saving download time and network resources.

The installer is one component in birthing machines.

Usage

By default, the installer will issue a DHCP request to discover the IP address for the machine and the address of a TFTP server from where it will fetch configuration data. If the config.json machine configuration file is already present, the configuration data are not fetched via TFTP. This mode supports iteratively writing the configuration data and testing the installer code itself.

In addition, the installer supports some sub-commands which may be used for building custom workflows and debugging. The basic usage pattern is:

installer [flags...] command [args...]

Built-in help is available with the command:

installer -h

The sub-commands available are:

• decode-base64: read base64-encoded data from the standard input and write the decoded data to the stdandard output
• dhcp-request: issue a DHCP request for debugging. The response data will be logged but no other action will be taken
• generate-random: generate pseudo-random data (NOT cryptographically secure) and write to standard output
• kexec-image: kexec into the kernel and initrd in the specified installer image. If the -tftpServerHostname is specified it will override what the installer may receive from the DHCP server
• list-images: list the images available on the imageserver
• load-configuration-from-tftp: load the configuration files from the TFTP server specified by -tftpServerHostname
• load-image: load the specified image and unpack it into the specified directory. The /dev, /proc, /sys and /tmp directories are bind-mounted in so that the image may be used in a chroot environment. This may be used to download a debugging image or it may be used by plugin programmes to download extra tools they require (in addition to the normal tools image)

When network booting, the hyper-control tool may be used to request that a nearby Hypervisor serve as a PXE server for the machine.

Status page

The installer provides a web interface on port 6978 which provides a status page, links to built-in dashboards and access to performance metrics and logs. If the installer is running on host myhost then the URL of the main status page is http://myhost:6978/. An RPC over HTTP interface is also provided over the same port. This port is only open while the machine is being installed. Once the machine starts booting into the new OS, the port will no longer be available.

Remote shell

The installer provides a remote shell (over RPC) interface which may be used for debugging, repairing failing installations and watching the progress of the installation. The hyper-control utility can be used to connect to the remote shell interface, using this command:

hyper-control installer-shell $hostname

where $hostname is the name/address of the machine running the installer.

Security

RPC access is restricted using TLS client authentication. The installer expects a root certificate in the file /etc/ssl/CA.pem which it trusts to sign certificates which grant access. It also requires a certificate and key which clients will use to validate the server. These should be in the files /etc/ssl/installer/cert.pem and /etc/ssl/installer/key.pem, respectively.

Configuration data

The following files are fetched from the TFTP server (or must already be present):

• config.json: the machine configuration. The schema is defined in the GetMachineInfoResponse type

• imagename: the name of the image to fetch from the imageserver and install on the machine (aka. the target OS)

• imageserver: the address of the imageserver

• storage-layout.json: the desired configuration of the storage devices. The schema is defined in the StorageLayout type

• tools-imagename: the name of an optional image containing tools that are required for custom configuration scripts. The default is to use the same image as used for the target OS, but a smaller, entirely different image can be used instead, providing a consistent environment for your configuration scripts regardless of the OS being installed

Sequence

The following sections describe the sequence of operations that the installer performs.

Update system time

Since some systems have an out-of-date clock (perhaps years in the past), the /build-timestamp file modification time is checked, and if the system clock is behind that time, the time is advanced to the timestamp file. This ensures that the system clock is at least no older than the time that the installer image was built.

Configure local network

The broadcast (EtherNet) interfaces are discovered and turned on. This gives some time for the links to become stable before active link detection is performed.

Load configuration

If the config.json file is present, the configuration is read immediately. No DHCP requests are performed and the -configurationLoader option is ignored. This is meant for development.

If the config.json file is not present, a DHCP request is issued to discover the IP address for the machine and the address of a TFTP server from where it may fetch configuration data. The primary network interface is configured based on the DHCP response. By default, the configuration files are downloaded from the TFTP server.

If the -configurationLoader option is given then the specified programme is run instead of fetching the configuration files from the TFTP server. This allows you to integrate into an existing system for publishing configuration data and converting to the format that the installer expects. The following command-line arguments will be provided:

1. The name of the directory where to write the configuration files
2. The name of the active (configured) network interface

If the -configurationBaseUrl option is given then the configuration is read from the specified server (typically a fleet-manager) instead of fetching the configuration files from the TFTP server. If the fleet-manager hostname is fleet-manager.prod then the base URL would be http://fleet-manager.prod:6977/tftpdata.

Discover storage

The storage devices are discovered and the image (without objects) is downloaded from the imageserver. An encryption key is generated.

The objects in the booted OS (typically netbooted) are scanned and checksummed and added to the object cache. The bulk of these will typically be the kernel image and modules.

If the -driveSelector option is given then the specified programme is run to select the drives that should be configured. The list of discovered, usable drives is provided as command-line arguments. The list of selected drives must be written to the standard output, one per line.

The boot device is scanned for an OS and if present is scanned and files are checksummed and added to the object cache. This can dramatically reduce the number of objects that need to be subsequently downloaded.

Objects for the target OS image not already in the cache are downloaded. This ensures that all objects are available prior to modifying the storage devices.

Load tools

The BusyBox-based image probably does not have all the tools necessary to configure the storage. By default, the target OS image is unpacked to the tmpfs directory specified by the -tmpRoot option. It should provide various utilities required for partitioning, encrypting and formatting storage devices.

If the tools-imagename file is present, the specified image is used instead.

Configure storage

The storage devices are erased (either with blkdiscard or by writing 1 MiB of zeros at the beginning) and the boot device is partitioned. Except for the partition which will contain the new root file-system, they are by default encrypted.

File-systems are created and the OS is installed on the root device. These operations are performed concurrently as these are typically I/O bound operations.

Mount points and entries in /etc/fstab are created for the non-root file-systems. The encryption key is written to the root file-system. The configuration files are written to the /var/log/installer directory.

Configure network

The broadcast interfaces are checked to see which have an active link (i.e. connected to an active switch port). The machine configuration is consulted and a network configuration file is rendered and written to the new root file-system. The configuration file specifies interfaces, trunks, VLANs and bridges. Further, the DNS configuration is written.

Alternatively, if the -networkConfigurator option is given then the specified programme is run instead to perform all network configuration. This allows you to provide an alternate implementation for configuring the target OS network. The following command-line arguments will be provided:

1. The name of the directory containing the previously downloaded configuration files
2. The root directory of the new OS file-system
3. The name of the active (configured) network interface
4. The root directory of the temporary target/tools OS environment

Copy installation logs

The installation logs are written to /var/log/installer/log.

Unmount storage

The storage devices are unmounted.

If the -completionNotifier option is given then the specified programme is run after the storage devices are unmounted. This allows you to signal to an external system that installation is complete and the new OS is about to be booted. The following command-line arguments will be provided:

1. The name of the directory containing the previously downloaded configuration files
2. The name of the active (configured) network interface

Reboot

If the -useKexec=true option was passed to hyper-control when requesting the network boot, the kexec utility is used to reboot into the new OS. Otherwise, the normal reboot system call is used, which causes a machine restart and a BIOS boot.

Example Configuration files

Machine configuration

An example config.json:

{
    "Machine": {
        "Hostname": "hyper0",
        "HostIpAddress": "192.168.1.2",
        "HostMacAddress": "de:ad:be:ef:00:01",
        "IPMI": {
            "Hostname": "hyper0-ipmi",
            "HostIpAddress": "192.168.0.2",
            "HostMacAddress": "de:ad:be:ef:00:00"
        },
        "Tags": {
            "RequiredImage": "hypervisor/2024-01-18:22:57:43",
            "Type": "SuperMicro Ultra"
        }
    },
    "Subnets": [
        {
            "Id": "Dev",
            "IpGateway": "192.168.100.1",
            "IpMask": "255.255.255.0",
            "DomainName": "dev.company.com",
            "DomainNameServers": [
                "192.168.1.53",
                "8.8.8.8"
            ],
            "Manage": true,
            "VlanId": 100
        },
        {
            "Id": "Hypervisors",
            "IpGateway": "192.168.1.1",
            "IpMask": "255.255.255.0",
            "DomainName": "hypervisors.company.com",
            "DomainNameServers": [
                "192.168.1.53",
                "8.8.8.8"
            ]
        },
        {
            "Id": "Prod",
            "IpGateway": "192.168.120.1",
            "IpMask": "255.255.255.0",
            "DomainName": "prod.company.com",
            "DomainNameServers": [
                "192.168.1.53",
                "8.8.8.8"
            ],
            "Manage": true,
            "VlanId": 120
        }
    ]
}

The rendered network configuration file will contain an interface with the primary IP address (192.168.1.2) with a default and DNS configuration taken from the matching subnet declaration (the Hypervisors subnet).

The IPMI information is used by the fleet-manager and hyper-control to identify the IPMI address to use for management operations.

Any EtherNet interfaces with active links will be trunked (if there are two or more) and VLAN and bridge interfaces added for each subnet declaration which has Manage set to true.

Storage layout

The default storage-layout.json is:

{
    "BootDriveLayout": [
        {
            "FileSystemType": "ext4",
            "MountPoint": "/",
            "MinimumFreeBytes": 2147483648
        },
        {
            "FileSystemType": "ext4",
            "MountPoint": "/home",
            "MinimumFreeBytes": 1073741824
        },
        {
            "FileSystemType": "ext4",
            "MountPoint": "/var/log",
            "MinimumFreeBytes": 536870912
        }
    ],
    "ExtraMountPointsBasename": "/data/",
    "Encrypt": true,
    "UseKexec": false
}

This will create:

• a root file-system with 2GiB of free space after the OS installation
• a /home file-system with 1 GiB free
• a /var/log file-system with 512 MiB free
• a /data/0 file-system consuming the remainder of the boot storage device
• zero or more /data/# file-systems for each secondary storage device

All the file-systems except for / will be encrypted. The kexec reboot method will not be used.

For each partition, the file-system label will be set to the value of MountPoint except for the following mount points:

• /: label will be rootfs
• /boot: label will be bootfs
• EFI system (/mnt/efi): label will be EFI

The label can be overridden by the FileSystemLabel field.

Signal handling

When run in daemon (installer) mode, the following signals are caught and the specified actions are taken:

• SIGCONT: rebooting is unpaused
• SIGHUP: the installer re-executes itself, running all the installation steps again
• SIGTSTP: rebooting is paused