Redhat Suite High Availability Overview

HIGH AVAILABILITY : Group of computer working together to provide the continuous availability of application service by eliminating single point of failure.
LOAD BALANCING : Distributed workloads across the multiple compute nodes.

High availability Requirement.
Single node .
dual NIC cards,
Dual RAID Controller,
Multipath  Shared Storage.
Both Primary and Secondary node should have
same hardware configuration,
Partition layout,
Software & Service should be same
except IP Address and hostname should be differ.

 OS Version Details – Redhat 6.4

SSH Passworless Access Maintain Correct Permission For Home Folder

How SSH passwordless key is working.
1) You need to create the public key/private key on the ssh client side.
2) Ssh server-side -> ssh client public/private key should present in the authorized key(/home/username/.ssh/authorized_keys.(it is like client-side key pair and server-side key pair both should match)
3) Should have correct permission /home/username should be 700 and SELinux should be disabled. If there is any permission mismatch key should not have accepted by the ssh server and it won’t work.
Above all the 3 rules matched then ssh passwordless will work without any problem.

NOTE: end of the public key you may have like username@hostname. From which host this key is created that username and hostname will be present. But using this you can do ssh passwordless from any machine to any not only to that specific machine.

Test Case: if there is any permission mismatch even though keypair is correct. Then we will get an issue like below. This is ssh -v verbose mode.

debug1: Next authentication method: publickey
debug1: Offering RSA public key: /home/jais/.ssh/id_rsa
debug1: Authentications that can continue: publickey,gssapi-keyex,gssapi-with-mic,password
debug1: Offering DSA public key: /home/jais/.ssh/id_dsa
debug1: Authentications that can continue: publickey,gssapi-keyex,gssapi-with-mic,password
debug1: Trying private key: /home/jais/.ssh/id_ecdsa
debug1: Trying private key: /home/jais/.ssh/id_ed25519
debug1: Next authentication method: password
Troubleshooting: This is client/server communication so, before troubleshooting, we need to find whether there is a problem on the server side or the client side.

 While doing ssh passworless access. Home directory .ssh should containt
700 permission it should not open for others like with permission (744).if it is open then we will get
error message
Permissions 0740 for '/home/username/.ssh/id_dsa' are too open.
It is required that your private key files are NOT accessible by others.
This private key will be ignored.
bad permissions: ignore key: /home/username/.ssh/id_dsa

[kamalr@admin ~]$ ls -l /home | grep jais

AMD Graphics Card Insallation Dependency Error

While I try to install the AMD driver I got the following dependency error.

--> Finished Dependency Resolution
Error: Package: xorg-x11-server-devel-1.19.3-11.el7.x86_64 (xorg)
           Requires: pixman-devel
Error: Package: xorg-x11-drv-libinput-0.25.0-2.el7.x86_64 (xorg)
Error: Package: xorg-x11-server-Xdmx-1.19.3-11.el7.x86_64 (xorg)
Error: Package: 1:xorg-x11-drv-amdgpu-pro-1.2.99-410326.x86_64 (amd)
           Requires: X11_ABI_VIDEODRV = 20.0
Error: Package: xorg-x11-server-Xephyr-1.19.3-11.el7.x86_64 (xorg)

Error: Package: xorg-x11-server-devel-1.19.3-11.el7.x86_64 (xorg)
           Requires: pkgconfig(dri) >= 7.8.0
Error: Package: xorg-x11-drv-libinput-0.25.0-2.el7.x86_64 (xorg)
Error: Package: xorg-x11-drv-libinput-0.25.0-2.el7.x86_64 (xorg)

Operating System Installation Vs Driver Installation.

While installation Operating system, Os itself install provisional driver for the specific hardware.Yet in some case advanced hardware setup like quadro 6000 DVI card rather than ordinary VGA Card ,in-build RAID storage controller.In that type of scenario we need to install driver manually after OS installation.

Example 1)Graphics Card Quadro 6000 DVI Card rather than the VGI Card.
First - Remove the Graphics card then install the operating system
Second - After OS installation, install Driver for Graphics Card and insert Physical Graphics Card into PCI slot.

Checklist Cluster Software Upgradation

What are things I have to do Before doing cluster software upgradation.  
Pre Upgrdation
1)Take a backup of old version
            a)important configuration file
            b)log parameter
            C)setting like PBS queue configuration, hook data.
 2)Upgrade the software.
Post Upgradation
3)Once upgrade check all the old parameter like queue hook node details everything configured. For example, in PAS after new installation FILE EXPIRATION date will be reset by default 14 days. So we need to change into at least max no of days or else all the old data will be deleted (Bala’s experience). NOTE: At any point in time if anything goes wrong we should ready to restore the data or else we will lose the confidence with customer.