Manage your server reboot with the OVHcloud Link Aggregation feature

Objective

This guide is designed to help you deploy all of the components and services you need to launch your OVHcloud solutions successfully in a fully private environment.
Get a private infrastructure without having to change the default configuration for your OVHcloud dedicated servers.

With OVHcloud dedicated servers, you can configure/declare your own networks.
Each server is equipped with at least 2 network interfaces, effectively functioning as aggregated links, ensuring redundancy in the event of failure.
You can therefore use/declare your public and private networks via our solution vRack.

We will present the case of dedicated server(s) configured in OLA mode, i.e. with only private networks. This choice offers your infrastructure the best possible isolation/protection for your hosted service.
The only significant difference is that private networks do not have access to everything that does not belong to your infrastructure.
As a result, a server isolated by its private network prevents the boot mechanism. This means that when systems are booted via the Netboot (Network Boot) method, they are based on OVHcloud’s internal network and shared services.

Netboot startup overview

A major component exists in 2 versions:

• PXE: Using a standardised client/server environment, based on BOOTP/DHCP/TFTP protocols, to enable boot/deployment through the client system network.
  
• iPXE: Using a more advanced, standardised client/server environment, based on HTTP, iSCSI, AoE, FCoE, Wi-Fi protocols to enable client system network boot/deployment.

A quick overview of Netboot startup at OVHcloud

List of components involved during startup:

• A DHCP server: Assigns a network configuration (lease with IP address) for a client machine that is attempting to boot.
• A TFTP service: Resources available across the network that will be queried by PXE and iXPE.
• The rEFInd solution, in the form of a BootLoader, was chosen because it was perfectly adapted. It will allow the search of boot sectors of client machines: local disk, USB, etc.

Here is a (logical) Netboot boot schema:

Requirements

• At least one dedicated server with an operating system already installed.
• An additional dedicated server with the default network interfaces configured, namely public and private network access. This server will host all services (DHCP and TFTP). The operating system will be one of your choice.
• You must have all of the network interfaces for this server in private mode, which implies that you have already configured our OLA feature.
  

OVHcloud Control Panel Access

• Direct link: Dedicated Servers
• Navigation path: Bare Metal Cloud > Dedicated servers > Select your server

Select your server and check that it is eligible for OLA: OVHcloud Link Aggregation in the Network interfaces tab.

Instructions

Deploy your DHCP and TFTP services

1. Install the packages for DHCP/TFTP services.
2. Perform the basic configuration for each service.
3. Turn on your server.

Below is an example of a basic private infrastructure (layer 2 diagram):

Example:

• Services hosted/shared on Node 0.
• Only one Node 1 client machine with active OLA.

DHCP service

Below is a sample configuration file for your DHCP service.
Depending on your distribution, the tree may be different (kea-dhcp4.conf).

In general, it is sufficient to:

• Declare a network interface for listening (waiting for requests).
• Specify the IP protocol version (v4 or v6).
• Enter a primary configuration file (as an example, see file below).

{
"Dhcp4": {
    "interfaces-config": {
        "interfaces": [ "eth1" ]
    },

    "control-socket": {
        "socket-type": "unix",
        "socket-name": "kea4-ctrl-socket"
    },

    "lease-database": {
        "type": "memfile",
        "lfc-interval": 3600
    },

    "expired-leases-processing": {
        "reclaim-timer-wait-time": 10,
        "flush-reclaimed-timer-wait-time": 25,
        "hold-reclaimed-time": 3600,
        "max-reclaim-leases": 100,
        "max-reclaim-time": 250,
        "unwarned-reclaim-cycles": 5
    },

    "renew-timer": 900,
    "rebind-timer": 1800,
    "valid-lifetime": 3600,

    "client-classes": [
        {
            "name": "iPXE script",
            "test": "option[user-class].exists and substring(option[user-class].hex,0,4) == 'iPXE' and option[client-system].hex == 0x0007", # Determines the type of architecture, in this case 64 bits
            "next-server": "192.168.1.1", # Determines the IP of your tftp server
            "boot-file-name": "refind.pxe",  # Determines the script loaded by the iPXE binary
        },
        {
            "name": "PXE UEFI",
            "test": "not option[user-class].exists and option[client-system].hex == 0x0007", # Determines the type of architecture, in this case 64 bits
            "next-server": "192.168.1.1", # Determines the IP of your tftp server
            "boot-file-name": "ipxe.efi" # Determines iPXE binary
        },
    ],

    "subnet4": [
        {
            "id": 1,
            "subnet": "192.168.1.0/28",
            "pools": [ { "pool": "192.168.1.2 - 192.168.1.14" } ],
            "option-data": [
                {
                    "name": "routers",
                    "data": "192.168.1.1"
                },
            ],
        }
    ],

    "loggers": [
    {
        "name": "kea-dhcp4",
        "output-options": [
            {
                "output": "stdout",
                "pattern": "%-5p %m\n",
            }
        ],
        "severity": "INFO",
        "debuglevel": 0
    }
  ]
}
}

Details:

• Private network (e.g. 192.168.1.0/28)
• subnet_mask: 255.255.255.240
• broadcast_address: 192.168.1.15
• dns_servers: See optional chapter
• ntp_servers: See optional chapter
• default_router : 192.168.1.1
• next-server: 192.168.1.1
• host: Client machine name
• hardware ethernet: Client machine hardware address (MAC)
• server-name: Client hostname machine

TFTP service

Depending on your distribution, there are several packages performing the TFTP server function.
For example: tftp-server, tftpd, tftpd-hpa or atftpd.

What you need to know:

• This service uses port 69 (UDP).
• It is mandatory to declare a "target" directory, corresponding to a local tree that will be used for receiving and downloading files.

Configuration example with tftpd-hpa software:

# /etc/default/tftpd-hpa
TFTP_USERNAME="tftp"
TFTP_DIRECTORY="/srv/tftp"
TFTP_ADDRESS="TFTP_server_address:69"
TFTP_OPTIONS="--secure"

We will use the path /srv/tftp as an example, and upload the necessary files:

root@node_0:/srv/tftp# tree
.
|-- ipxe.efi
|-- refind.conf
|-- refind.pxe
`-- refind_x64.efi

The rEFInd bootloader

• File contents refind.pxe:

#!ipxe

echo Boot to local disk

iseq ${platform} efi && goto is_efi_x86_64 || goto end

:is_efi_x86_64
echo EFI boot mode

# Retrieve configuration file
imgfetch --name refind.conf tftp://${next-server}/refind.conf

# Load rEFIND binary
imgfetch --name refind tftp://${next-server}/refind_x64.efi
chain refind

:end
echo Chain on hard drive failed
sleep 10
exit 1

• File contents refind.conf:

This involves integrating the minimum guidelines for proper integration with OVHcloud SI.

timeout 1
default_selection 1
hideui hwtest
hideui hints
banner_scale
textonly
scanfor internal
uefi_deep_legacy_scan
scan_delay 0

Getting started

Below is a preview of what you get when displaying a UEFI Netboot (default):
Corresponds to steps 1 through 8.

Corresponds to the result of steps 8 and 9.

Above, we have the rEFInd bootloader loaded on a machine with a debian system installed.

You will find on this link the resources used to develop our tests and examples throughout this presentation. They can be used as templates, depending on your needs.

Optional

We also recommend deploying DNS and NTP services.

These are not necessary for the system startup phases, so not imposed in this procedure. They are, however, among the services that will be important in the future, especially for the stability of your infrastructure.

Service DNS

You can use the local table for each Node, i.e. the /etc/hosts file, or you can use a service like dnsmasq.

Service NTP

It is strongly recommended that you use an NTP service, especially if your infrastructure includes several machines.

• List of ports to authorise on your local firewall (on the machine hosting the services):
  • NTP port 123
  • DNS port 53

Go further

Understanding and customising your DHCP service
Understanding and customising your iPXE service
Understanding and customising your rEFInd service
Discovering and understanding NTP
Discovering and understanding Dnsmasq

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