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(2) Physical Server

(1)PhysicalNICIPMI(2)PhysicalServerPXE(3)VirtualContainerKubernetes(4)VirtualVMOpenStack(1)PhysicalNIC

Interface​

The physical servers are bootstrapped via PXE. PXE is a firmware that runs on NIC and is able to chainload arbitrary code. In this case a more powerful version of PXE is chainloaded (iPXE) which subsequently installs/boots the desired OS via network. The primary technologies that enables this process include dhcp, tft and http. The following graph showcases the boot process in a simplified manner:

BIOSPXEROMNetworkCardiPXEOperatingSystemDHCP/TFTPServerWebserverBootingNodeSeedNodeDHCP:networkconfg;iPXEbinarypathTFTP:iPXEbinaryDHCP:networkconfg;iPXEscriptpathHTTP:iPXEscriptreferencingkernel/rootFSURLHTTP:kernel/rootFSHTTP:generatedprovisioningscriptsnetworkbootchainloadiPXEloadkernel

COTB Implementation​

The actual OS bootstrapped via network is heavily customized by COTB. The customer specific settings are specified in the inventory. Moreover, this layer specifically enables the API for its upper layer, namely Kubernetes.