Healthy Compute Node Boot Process
In order to investigate node boot-related issues, it is important to understand the flow of a healthy boot process and the associated components. This section outlines the normal flow of components that play a role in booting compute nodes, including DHCP, BSS, and TPTP.
DHCP
A healthy DHCP exchange between server and client looks like the following:
| Traffic | Description | Sender |
|---|---|---|
| DHCP Discover | A broadcast request from the client requesting an IP address. The request contains the client’s MAC address. | Client |
| DHCP Offer | The server offers an IP address to the client. | Server |
| DHCP Request | After testing the IP address to see that it is not in use, the client requests the proffered IP address. | Client |
| DHCP ACK | The server acknowledges that the client owns the lease on the IP address. | Server |
The following figure shows what a healthy DHCP discover process looks like via Wireshark, which is a packet analyzer:
The DHCP client uses port 68, whereas the DHCP server uses port 67. Unlike most Kubernetes pods, the DHCP pod is located on the host network.
TFTP
A healthy TFTP exchange between server and client looks like the following.
| Traffic | Description | Sender |
|---|---|---|
Read Request File: filename tsize=0 |
The client requests a file with a tsize equal to zero. |
Client |
Option Acknowledgement |
The server acknowledges the request and provides the file’s size and block transfer size. | Server |
Error Code, Code: Option negotiation failed, Message: User aborted the transfer |
The client aborts the transfer once it determines the file size. | Client |
Read Request File: filename |
The client requests the file again. | Client |
Option Acknowledgement |
The server acknowledges the request and provides the block transfer size. | Server |
Acknowledgement, Block: 0 |
The client acknowledges the server. | Client |
Data Packet, Block: 1 |
The server sends the first data packet. | Server |
Acknowledgement, Block: 1 |
The client acknowledges reception of block 1. | Client |
The last two steps repeat until the file transfer is complete. The last block from the server will be labeled as (Last). The TFTP server listens on port 69. Kubernetes forwards port 69 on every node in the Kubernetes cluster to the TFTP pod.
Boot Script Service (BSS)
A healthy transaction with the Boot Script Service (BSS) looks similar to the following:
ncn-mw# cray bss bootscript list --mac a4:bf:01:3e:c0:a2
Example output (lines truncated because of extreme length):
#!ipxe
kernel --name kernel http://rgw.local:8080/boot-images/29c2cc23-a9d6-4e9a-ab1a-b5fa9270c975/kernel?X-Amz-A...
initrd --name initrd http://rgw.local:8080/boot-images/29c2cc23-a9d6-4e9a-ab1a-b5fa9270c975/initrd?X-Amz-A...
boot || goto boot_retry
:boot_retry
sleep 30
chain https://api-gw-service-nmn.local/apis/bss/boot/v1/bootscript?mac=a4:bf:01:3e:f9:28&retry=1