• Troubleshoot Kubernetes service not being resolved

  When you create a Kubernetes Service, pods from within the same namespace should be able to resolve it's IP by name. For example, if we create a service named ampa-votacions; any pod from the same namespace should be able to resolve it's IP. But sometimes it can't be resolved:

  $ kubectl exec -it ampa-install-ws7cw -- sh
  / $ nslookup ampa-votacions
  Server:   172.20.0.10
  Address:  172.20.0.10:53
  
  ** server can't find ampa-votacions.us-west-2.compute.internal: NXDOMAIN
  
  ** server can't find ampa-votacions.ampa.svc.cluster.local: NXDOMAIN
  
  ** server can't find ampa-votacions.svc.cluster.local: NXDOMAIN
  
  ** server can't find ampa-votacions.ampa.svc.cluster.local: NXDOMAIN
  
  ** server can't find ampa-votacions.cluster.local: NXDOMAIN
  
  ** server can't find ampa-votacions.svc.cluster.local: NXDOMAIN
  
  ** server can't find ampa-votacions.cluster.local: NXDOMAIN
  
  ** server can't find ampa-votacions.us-west-2.compute.internal: NXDOMAIN
  

  19/04/2021

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• Terraform output values

  To be able to save data generated using terraform to be able to import the terraform state somewhere else using terraform_remote_state or retrieving it using the CLI we need to use the output directive:

  output "alb_dns_name" {
    description = "ALB DNS name"
    value       = aws_alb.jenkins-alb.dns_name
  }
  

  16/04/2021

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• JVM heap options: Xmx and Xms

  The Xmx and Xms settings are most commonly overlooked settings but yet quite critical for the JVM to perform as expected. They control the JVM's heap: the memory area where objects are instantiated.

  15/04/2021

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• kubectl drain: prepare node for maintenance

  You can use kubectl drain to evict pods from a node and mark it as unschedulable to prevent new pods from arriving. It will allow the pod's containers to gracefully terminate and respecting the PodDisruptionBudgets with a few exceptions. Let's test it suing the following nodes:

  $ kubectl get nodes
  NAME                    STATUS   ROLES                  AGE   VERSION
  nauvoo.pet2cattle.com   Ready    control-plane,master   19d   v1.20.4+k3s1
  tycho.pet2cattle.com    Ready    <none>                 26s   v1.20.4+k3s1
  

  14/04/2021

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• How kubernetes hides away the volumeMounts complexity

  If we try compare volumeMounts with the actual mounts that we have on a pod using, for example, df it can be quite confusing due to the usage of the overlay filesystem

  Let's consider the volumeMounts section of a deploy:

  $ kubectl get deploy pet2cattle -o yaml
  (...)
            volumeMounts:
            - mountPath: /opt/pet2cattle/conf
              name: config
            - mountPath: /opt/pet2cattle/data
              name: pet2cattle
              subPath: data
            - mountPath: /opt/pet2cattle/lib
              name: pet2cattle
              subPath: lib
            - mountPath: /tmp
              name: tmp-dir
  (...)
  

  And compare it with the filesystem we see on the pod:

  $ kubectl exec pet2cattle-8475d6697-jbmsm -- df -hP
  Filesystem      Size  Used Avail Use% Mounted on
  overlay         100G  9.7G   91G  10% /
  tmpfs            64M     0   64M   0% /dev
  tmpfs           3.9G     0  3.9G   0% /sys/fs/cgroup
  /dev/xvda1      100G  9.7G   91G  10% /tmp
  shm              64M     0   64M   0% /dev/shm
  /dev/xvdcu       20G  2.5G   18G  13% /opt/pet2cattle/lib
  tmpfs           3.9G   12K  3.9G   1% /run/secrets/kubernetes.io/serviceaccount
  tmpfs           3.9G     0  3.9G   0% /proc/acpi
  tmpfs           3.9G     0  3.9G   0% /proc/scsi
  tmpfs           3.9G     0  3.9G   0% /sys/firmware
  

  13/04/2021

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