Tools

[Git] Change case of a folder name

Git / 2023 年 8 月 19 日

Make sure you have the ignorecase set to false:

git config core.ignorecase false

Then, do two git mv:

git mv foldername tempname
git mv tempname folderName

[Git] Change commit author

Git / 2023 年 1 月 12 日

Use git rebase to select commits you want to modify

git rebase -i --root

And then for each rebase step, execute the following:

git commit --amend --reset-author --no-edit
git rebase --continue

[Git] Git submodule basic commands

Git / 2022 年 8 月 8 日
  • Clone a repo tree
git clone --recurse-submodules remote_url
  • Link a submodule
git submodule add submodule_remote_url local_linking_path
# Then commit & push to the main repo
  • Pull from a submodule
# Pull from specific branch
git pull --recurse-submodules my-branch
# Then commit & push to the main repo
  • Update a submodule
cd submodule_path
# Do the commits and push normally, the changes will be pushed to submodule repo

cd main
# Then do a commit and push to the main module
  • Reset submodule head to currently stored reference
git submodule update --init

[K8s] Command cheatsheet

K8s / 2022 年 5 月 24 日
  • View config
kubectl config view
  • Show cluster info
kubectl cluster-info

# Example output
Kubernetes control plane is running at https://10.0.0.9:8443
KubeDNS is running at https://10.0.0.9:8443/api/v1/namespaces/kube-system/services/kube-dns:dns/proxy
  • Get component info
kubectl get xxx -o wide -A
kubectl describe xxx

# Use -l $LABEL to filter using labels
# USe --show-labels to show labels

# xxx can be nodes, pods, deployments,
# events, services, replicaset, etc.
# To specify a specific object: xxx/name. For example: deloy/my-deploy

# For full list and the short names, do 
kubectl api-resources
  • Create/Edit/Delete any object
# Create
kubectl create -f config.yaml

# Edit. Can be used to rollout a new version when editing deployments
kubectl edit xxx/$NAME

# Delete
kubectl delete xxx/$NAME
kubectl delete -f config.yaml
  • Create a deployment which manages a Pod
kubectl create deployment hello-node --image=k8s.gcr.io/echoserver:1.4
  • Expose a deployment as a service
# 8080 here is the container port
# NodePort exposes the ports on each node running related pods
kubectl expose deployment/hello-node --type="NodePort" --port 8080
  • Scale a deployment
kubectl scale deployments/kubernetes-bootcamp --replicas=4
  • Update a deployment
kubectl set image deployments/kubernetes-bootcamp kubernetes-bootcamp=jocatalin/kubernetes-bootcamp:v2 --record=true

# Check the rollout status
kubectl rollout status deployments/kubernetes-bootcamp

# Undo the rollout
# This rollback to previous replicaset
kubectl rollout undo deployments/kubernetes-bootcamp
  • Undo a rollout
# Find the replicaset you want to restore
# (default 10 history replicasets are saved)
kubectl get rs -o wide
kubectl rollout history $DEPLOY

# Get the revision number of the desired replicaset
kubectl describe rs kubernetes-bootcamp-fb5c67579

# Rollback to the specific replicaset
kubectl rollout undo deployments/kubernetes-bootcamp --to-revision=2
  • Logging
kubectl logs $POD_NAME
  • Execute a command on a container in a Pod
kubectl exec $POD_NAME -- $COMMAND


# Start a bash session. If no container specified, kubectl.kubernetes.io/default-container will be used
kubectl exec -it $POD_NAME -c $CONTAINER_NAME -- bash
  • Access a Pod’s port locally w/o services (for debugging)
# Method 1. Port-forwarding
kubectl port-forward POD_NAME HOST_PORT:POD_PORT
# Then you can access the endpoint at 
# localhost:HOST_PORT

# Method 2. Proxy
kubectl proxy
# Then you can access the endpoint at
# http://localhost:8001/api/v1/namespaces/default/pods/$POD_NAME:$POD_PORT/proxy/
  • Labeling
# Attach a new label
kubectl label pods $POD_NAME version=v1

# View labels of a Pod
kubectl describe pods $POD_NAME
  • Secrets
    Ways to use secrets:
    • As container envs (secretKeyRef)
    • As volumes mounted to containers
    • Save to a docker image and provide access inside the cluster
# Create a secret
kubectl create secret generic $SECRET [--from-file file_name] [--from-literal]

# Show a secret
kubectl get secret/xxx -o json
  • ConfigMap
kubectl create configmap $CONFIGMAP [--from-file] [--from-literal]
  • Drain a Node
# Drain a Node to move all Pods to other Nodes
kubectl drain $NODE

# Undo draining
kubectl uncordon $NODE to revert
  • Clean up
kubectl delete service hello-node
kubectl delete deployment hello-node
minikube stop
minikube delete

[K8s] Basic concept notes

K8s / 2023 年 2 月 22 日

Main components

Source
  • Each Node (machine) includes a kubelet and many Pods
  • Kubelets communicate with the Control Plane (actually a special node) and the corresponding Pods inside the Node
  • Control Plane can be split into multiple machines
  • Each Pod serves as an application and has many containers which are tightly coupled
  • Containers inside the same Pod share the same networking resource
  • kube-apiserver: Exposes the Kubernetes API
  • etcd: Key value store
  • kube-scheduler: Schedule Nodes to run Pods
  • kube-controller-manager: Many components deal with monitoring, task running, and account access control

History of container runtime

Source
  • From the oldest method (top) to newest approach (bottom)
  • CRI is an interface designed for kubelet to manipulate containers
  • Any CRI-compliant container runtime can do the job: Docker Engine, containerd, CRI-O, …
  • OCI runtime: runC, runhcs, …

K8s entity concepts

Source
  • A Deployment checks on the health of your Pod and restarts the Pod’s container if it terminates. Deployments are the recommended way to manage the creation and scaling of Pods
  • Deployment configuration file works very similar to docker-compose.yml
  • Deployment controller automatically search for a suitable node where an instance of the application could be run
  • If the Node hosting an instance goes down or is deleted, the Deployment controller replaces the instance with an instance on another Node in the cluster
  • A Service is an exposed Deployment, which encapsulates a set of Pods called ReplicaSet
  • Secrets and ConfigMap are extra resources we can mount into containers
  • Volumes types:
    • emptyDir: Storage lives with a Pod
    • hostPath: Storage lives with a Node
    • NFS and other cloud provider type
  • Storage
    • Storage Classes: Templates to create volumes
    • Persistent Volume Claims: Create (or use existing) PV by specifying SC, size, read/write type etc. We can then attach a PVC into a Pod config
    • Persistent Volumes: Either created manually (static) or automatically (dynamic) when no any PV match the claim
  • Resource
    • Request: minimum requirement
    • Quota: maximum limit

Common tools

  • cri-o: A container runtime
  • kubelet: Starts pods and containers
  • kubectl: The command line util to talk to your cluster.
  • kubeadm: The command to bootstrap the cluster (control planes etc.)
  • minikube: A tool to quickly setup a single-node cluster inside a VM
  • Kops: Setup AWS clusters easily

Networking

  • Each Node has its own node IP (as normal machines) which is mainly accessed by the control plane node
  • Each Pod has its own IP, where the Node will forward the request to
  • Pods inside each Node, or across Nodes, can see each other using Pod IPs, but not recommended to do so. Exposing the endpoint as a service is preferred
  • Containers inside the same Pod can refer to each other using localhost:port, this is like running up docker-compose inside a “pod machine”, but the container network is configured as host
  • Services have Cluster IPs and domain name, for intra-cluster access
  • Port definitions:
    • port: For intra-cluster access
    • nodePort: Exposed port on the Node
    • targetPort: Container port
  • Ingress along with ingress controller act like an Nginx load balancer. The DNS record should point to this load balancer IP to serve services across multiple Nodes

[Git] Show logs for specific branch

Git / 2022 年 4 月 14 日

If you have master merged into your current branch, your git log will be messy because it also shows the commits from the master.

If you want to show your branch logs, use the following command:

git log master..

or

git log master..mybranch

* git log a..b actually means “includes commits that are (backward) reachable from b but exclude those that are reachable from a”

[Git] Resolve conflicts for git stash pop

Git / 2020 年 7 月 30 日

Assume you have conflicts after executing git stash pop:

  1. Resolve the conflicts manually by yourself
  2. Use git reset to mark conflicts as resolved
  3. Drop the stash using git stash drop because git doesn’t do it if conflicts occur

[Git] Cut commits onto other branches using git rebase –onto

Git / 2022 年 6 月 1 日

Assume we have following branches:

We want to cut commit_3 and commit_4 on branch_2, onto master (commit_2). We can use the commands:

git checkout branch_2
git rebase --onto b111dc9 34e3359
(git rebase --onto new_base old_base)

The result looks like this:

If we want the commits but not to modify the incoming branch (branch_2 in the above example), we can use cherry-pick :

git checkout master
git cherry-pick 34e3359..321b7c0
(git cherry-pick start_commit_not_included..end_commit_included)