Month: March 2023

irqbalance or set_irq_affinity – interesting cause for a network performance issue.

When it comes to high-performance computing, squeezing every bit of performance out of the system is crucial. One of the critical factors in achieving high performance is reducing system latency. Interrupt requests (IRQs) are a type of signal generated by hardware devices that require attention from the CPU. By default, IRQs can be delivered to any CPU core in a multi-core system. This can lead to cache misses and contention, ultimately leading to increased latency. Fortunately, there are tools available to help manage IRQ affinity and reduce latency, such as irqbalance and set_irq_affinity. https://github.com/majek/ixgbe/blob/master/scripts/set_irq_affinity

irqbalance is a Linux daemon that helps to balance IRQs across multiple CPU cores to reduce latency. By default, irqbalance distributes IRQs across all CPU cores, which is a good starting point. However, depending on the system configuration, it may be necessary to adjust IRQ affinity further to optimize performance.

set_irq_affinity is a script that allows users to set IRQ affinity for specific hardware devices. The script can be used to specify which CPU cores should receive IRQs for a specific hardware device, reducing the chance of cache misses and contention. Set_irq_affinity requires root access to run and must be executed for each device on the system.

To use set_irq_affinity, first, identify the device’s IRQ number using the “cat /proc/interrupts” command. Once the IRQ number has been identified, run the set_irq_affinity script, specifying the IRQ number and the desired CPU cores. For example, to set the IRQ affinity for IRQ 16 to CPU cores 0 and 1, run the following command:

sudo set_irq_affinity.sh 16 0-1
This command tells the kernel to route IRQ 16 to CPU cores 0 and 1.

Keep in mind that setting IRQ affinity is a delicate balance. Setting IRQ affinity for too few CPU cores can result in increased latency due to increased contention for those cores. On the other hand, setting IRQ affinity for too many CPU cores can result in inefficient cache usage and increased latency due to cache misses.

In summary, managing IRQ affinity is an important aspect of optimizing system performance, particularly in high-performance computing environments. The irqbalance daemon can help to balance IRQs across multiple CPU cores, while set_irq_affinity allows users to specify the IRQ affinity for specific hardware devices. By carefully managing IRQ affinity, users can reduce latency and achieve better system performance.

Clean up your old Kubernetes persistent data!

If you have ever removed a node from a Kubernetes cluster and then added it back, you may have encountered some issues with persistent data. Persistent data is any data that survives beyond the lifecycle of a pod, such as databases, logs, or configuration files. Kubernetes uses persistent volumes (PVs) and persistent volume claims (PVCs) to manage persistent data across the cluster.

However, sometimes these resources may not be cleaned up properly when a node is deleted or drained. This can cause problems when you try to reuse the node for another cluster or add it back to the same cluster. For example, you may see errors like:

  • Failed to attach volume \”pvc-1234\” on node \”node1\”: volume is already attached to node \”node2\”
  • Failed to mount volume \”pvc-5678\” on pod \”pod1\”: mount failed: exit status 32
  • Failed to create subPath directory for volumeMount \”data\” of container \”db\”: mkdir /var/lib/kubelet/pods/abcd-efgh/volumes/kubernetes.io~nfs/data: file exists

To avoid these issues, you need to clean up your old Kubernetes persistent data before adding a node back to a cluster. Here are some steps you can follow:

Step 1: Delete or unbind any PVCs associated with the node

The first step is to delete or unbind any PVCs that are associated with the node you want to remove. A PVC is a request for storage by a user or a pod. It binds to a PV that provides the actual storage backend. When you delete a PVC, it also releases the PV that it was bound to, unless the PV has a reclaim policy of Retain.

To list all the PVCs in your cluster, you can use the command:

kubectl get pvc --all-namespaces

To delete a PVC, you can use the command:

kubectl delete pvc <pvc-name> -n <namespace>

Alternatively, you can unbind a PVC from a PV without deleting it by editing the PVC spec and removing the volumeName field. This will make the PVC available for binding to another PV.

To edit a PVC, you can use the command:

kubectl edit pvc <pvc-name> -n <namespace>

Step 2: Delete any PVs that are not bound to any PVCs

The next step is to delete any PVs that are not bound to any PVCs. A PV is a piece of storage in the cluster that has been provisioned by an administrator or dynamically provisioned using storage classes. It is a resource in the cluster just like a node. PVs have a lifecycle independent of any pod that uses them.

To list all the PVs in your cluster, you can use the command:

kubectl get pv

To delete a PV, you can use the command:

kubectl delete pv <pv-name>

Note that deleting a PV does not necessarily delete the underlying storage device or volume. Depending on the type of storage and the reclaim policy of the PV, you may need to manually delete the storage device or volume from your cloud provider or storage server.

Step 3: Delete any leftover data on the node

The final step is to delete any leftover data on the node that you want to remove. This may include directories or files that were created by Kubernetes or by your applications. For example, you may need to delete:

  • The /etc/cni/net.d directory that contains CNI (Container Network Interface) configuration files
  • The /var/lib/kubelet directory that contains kubelet data such as pods, volumes, plugins, etc.
  • The /var/lib/etcd directory that contains etcd data if the node was running an etcd member
  • The /var/lib/docker directory that contains docker data such as images, containers, volumes, etc.
  • Any other application-specific data directories or files that were mounted or created on the node

To delete these directories or files, you can use commands like:

sudo rm -rf /etc/cni/net.d
sudo rm -rf /var/lib/kubelet
sudo rm -rf /var/lib/etcd
sudo rm -rf /var/lib/docker
sudo rm -rf /path/to/your/application/data

Be careful when using these commands and make sure you are deleting only what you intend

Source: Conversation with Bing, 3/27/2023(1) A complete storage guide for your Kubernetes storage problems. https://bing.com/search?q=Kubernetes+persistent+data Accessed 3/27/2023.
(2) Persistent Volumes | Kubernetes. https://kubernetes.io/docs/concepts/storage/persistent-volumes/?ref=hack-slash Accessed 3/27/2023.
(3) Kubernetes Persistent Volumes – Ultimate Guide – Knowledge Base by …. https://phoenixnap.com/kb/kubernetes-persistent-volumes Accessed 3/27/2023.
(4) Data persistence on Kubernetes – SQL Server Big Data Clusters. https://learn.microsoft.com/en-us/sql/big-data-cluster/concept-data-persistence?view=sql-server-ver15 Accessed 3/27/2023.
(5) A complete storage guide for your Kubernetes storage problems. https://www.cncf.io/blog/2020/04/28/a-complete-storage-guide-for-your-kubernetes-storage-problems/ Accessed 3/27/2023.
(6) Data Persistence in Kubernetes | Kubernetes Volumes simply explained …. https://dev.to/techworld_with_nana/data-persistence-in-kubernetes-kubernetes-volumes-simply-explained-852 Accessed 3/27/2023.

Use a password manager!

In today’s digital age, where we have an online presence for almost everything, from social media to banking, it’s essential to keep our personal information secure. One of the most crucial aspects of online security is using strong and unique passwords for every website. However, with the growing number of online accounts, it can be challenging to remember all the passwords. That’s where password managers come in.

A password manager is a software that stores your passwords securely in an encrypted database. It creates and stores unique, strong passwords for every website you use, so you don’t have to remember them. Instead, you only need to remember one master password to access your password manager.

Using a password manager offers many benefits. Firstly, it eliminates the need to remember multiple passwords, which can be a daunting task, especially when you’re using complex passwords. Secondly, it saves you time since you don’t have to waste time resetting passwords or trying to remember them. Thirdly, it helps protect against phishing attacks, as the password manager only fills in passwords for legitimate websites. Finally, it provides an additional layer of security, as password managers generate random, complex passwords that are much harder to guess or crack.

While using a password manager is undoubtedly beneficial, it’s important to remember that it’s not a silver bullet for online security. It’s crucial to choose a strong and unique master password, preferably a passphrase that’s easy to remember but difficult for others to guess. You should also enable two-factor authentication, which requires you to enter a code sent to your phone or another device to access your account.

Another important aspect of online security is to never write down passwords or store them in unencrypted files. Writing down passwords and leaving them in plain sight can make it easy for someone to gain access to your accounts. If you must write down a password, store it in a secure location like a locked safe.

Finally, it’s important to use a different password for every website. This may seem like a hassle, but it’s crucial for security. If you use the same password for multiple accounts and a hacker gains access to one, they can easily access all your accounts. By using unique passwords for every website, you limit the damage that a data breach can cause.

Using a password manager is an excellent way to stay secure online. It eliminates the need to remember multiple passwords, saves time, and provides an extra layer of security. However, it’s important to use a strong and unique master password, enable two-factor authentication, and avoid writing down passwords. By taking these precautions, you can help protect yourself from the increasing number of online threats.

There are several popular password managers available, each with its own unique features and capabilities. Here are some examples of popular password managers:

  1. LastPass: LastPass is a popular password manager that offers both free and paid versions. It can generate strong, unique passwords and store them securely, as well as autofill login credentials on websites and applications.
  2. 1Password: 1Password is another popular password manager that offers features like password generation, secure storage, and autofill. It also includes a digital wallet for storing credit card information and secure notes.
  3. Dashlane: Dashlane is a user-friendly password manager that offers both free and paid versions. It can generate and store strong passwords, autofill login credentials, and provide secure sharing of passwords with trusted family and friends.
  4. KeePass: KeePass is a free, open-source password manager that allows you to store passwords in an encrypted database. It has plugins available for additional features and supports two-factor authentication.
  5. Bitwarden: Bitwarden is a free, open-source password manager that offers both desktop and mobile applications. It can generate strong passwords, store them securely, and autofill login credentials on websites and applications.
  6. MacPass: MacPass is a free, open-source password manager that is specifically designed for macOS. It stores passwords in an encrypted database and supports two-factor authentication.
  7. KeePassXC: KeePassXC is a community-driven, open-source password manager that is compatible with multiple platforms, including Windows, macOS, and Linux. It offers features like password generation, secure storage, and autofill.

There are many password managers available, each with its own unique features and benefits. It’s essential to choose a password manager that meets your specific needs and preferences to help keep your online accounts secure.