add a diagram with the boot process

admin-guide/deployment/_static/legacy_boot.puml

@@ -0,0 +1,79 @@
+@startuml
+
+actor admin 
+participant "BIOS Node\n(legacy boot)" as bootnode
+participant "QIP DHCP" as dhcp
+participant "pxeserv01.psi.ch" as pxeserver
+participant "boot00.psi.ch" as sysdb
+participant "repo00.psi.ch" as reposerver
+
+admin -> bootnode : boots up
+
+hnote over bootnode
+    BIOS
+endhnote
+bootnode -> dhcp : DHCP request
+dhcp -> bootnode : IP + PXE boot location
+bootnode -> pxeserver : load PXE kernel tftp:/tftpboot/pxelinux.0
+
+hnote over bootnode
+    PXE
+endhnote
+bootnode -> pxeserver : load PXE config tftp:/tftpboot/pxelinux.cfg/01-$MAC
+note right
+    By manually setting a MAC or IP config the 
+    boot menu can be customised or shortcut. 
+    Most is managed by symlinks. There is the 
+    undocumented "link-to-lxprod.py" script for
+    manually linking MAC to hostname and hostname
+    to "lxprod". At some places this is done the
+    opposite by linking hostname to MAC to "lxprod".
+    Having the **link to "lxprod" loads directly**
+    **the iPXE kernel "boot00.lkrn"**, shortcutting
+    the manual selection below.
+end note
+bootnode -> pxeserver : load PXE config tftp:/tftpboot/pxelinux.cfg/$HEX-IP
+bootnode -> pxeserver : load PXE config tftp:/tftpboot/pxelinux.cfg/default
+note right
+    **Default selection is local boot**,
+    but also visible and manually selectable are
+    - Red Hat 7 Network Install
+    - Windows Network install
+    and many more which are hidden, but can 
+    be selected from the prompt, some with
+    comments from 2013.
+end note
+admin -> bootnode :  selects "Red Hat 7 Network Install"
+bootnode -> pxeserver : load iPXE kernel tftp:/tftpboot/boot00.lkrn
+note right
+    https://git.psi.ch/linux-infra/ipxe-build
+    The following steps are by embed/pxe.ipxe
+end note
+
+hnote over bootnode
+    iPXE
+endhnote
+bootnode -> dhcp : DHCP request
+dhcp -> bootnode : IP
+bootnode -> sysdb : load iPXE menu http:/ipxe/v1/config?mac=$MAC
+note right
+    Default selection by sydb boot 
+    property "local" or "netboot",
+    later installs Red Hat 7.9.
+    manually selectable are all 
+    Red Hat 7 versions to install,
+    Windows, a selection of tools
+    and "HP SPP".
+endnote
+bootnode -> reposerver : load initrd http:/iso/rhel-server-7.9-x86_64-dvd/images/pxeboot/initrd.img
+bootnode -> reposerver : load kernel http:/iso/rhel-server-7.9-x86_64-dvd/images/pxeboot/vmlinuz
+
+hnote over bootnode
+    Linux kernel
+endhnote
+bootnode -> reposerver : installation media http:/iso/rhel-server-7.9-x86_64-dvd/ 
+bootnode -> sysdb : kickstart file http:/kickstart/v1/config?fqdn=$HOSTNAME&instrepo=rhel-server-7.9-x86_64-dvd
+
+@enduml
+
+

admin-guide/deployment/ipxe.rst

@@ -32,6 +32,11 @@ which distribution it is supposed to use. The menu offers other options as well,
 e.g. an interactive iPXE shell and a memory test.
 
 
+Sequence Diagram of the BIOS (Legacy) Boot Process
+--------------------------------------------------
+.. image:: _static/legacy_boot.png
+
+
 Building the iPXE boot image
 ----------------------------