Docker cheat sheet

Create a DockerFile

At the root of your project, create a file name DockerFile, without any file extension. 

In workdir you put the absolute path to your app.

FROM node:12-alpine
COPY . .
RUN yarn install --production
CMD ["node", "/app/src/index.js"]

Build an image

Cd in the directory where your DockerFile is and run:

$sudo docker build -t getting-started .

Don’t forget the “.”  at the end of the command!

getting-started is the name of the app you are creating in docker. It will be the name of the image.

Run the image in a container

$sudo docker run -dp 3000:3000 getting-started

-p 3000:3000 is mapping the internal port 3000 (the 2nd one) to the external port 3000(the first one). So you will be able to access your app on localhost:3000.

Update an image

First you need to remove the container. For that you will need the container id:

you can get it in two different ways:

$sudo docker ps


$sudo docker container ls

that gives you the container process id. You can then stop the container:

$sudo docker stop 123456789

and then remove the container:

$sudo docker rm 123456789

You can also do that in one line by using the force option to close and remove the container in one go:

$sudo docker rm -f 123456789 

Sharing docker image:

You’ll need a docker account in 

Create a repository.

Once the repository is created, you’ll see a Docker command example to push your project in the repo:

$docker push username/getting-started:tagname

Persistency between restarts

To have data persitency between restart, you will need to mount a volume in the container. That volume will be available from the host but also from container that has mounted the same volume.

Create a volume

$sudo docker volume create todo-db

Mount the volume to the container

$sudo docker run -dp 3000:3000 -v todo-db:/etc/todos getting-started

Now your data will persist between session.

Where the data are actually stored on the disk?


$sudo docker volume inspect todo-db

It will return:



        “CreatedAt”: “2019-09-26T02:18:36Z”,

        “Driver”: “local”,

        “Labels”: {},

        “Mountpoint”: “/var/lib/docker/volumes/todo-db/_data”,

        “Name”: “todo-db”,

        “Options”: {},

        “Scope”: “local”



The mountpoint is the actual location of the data on the host.

Watch changes on a simple refresh rather than rebuilding the app:

use bind mount. 

Example command:

$docker run -dp 3000:3000 \
    -w /app -v ${PWD}:/app \
    node:12-alpine \
    sh -c "yarn install && yarn run dev"

You can check the logs: 

$docker logs -f <container-id>

Run MySql on a separate container

Why not put it in the same container as your app? It’s because you  might not want to ship your development db with your app. You might also want to scale the front-end and the back-end up differently.

1- create a network:

$sudo docker network create todo-app
$docker run -d \
   --network todo-app --network-alias mysql \
    -v todo-mysql-data:/var/lib/mysql \
    -e MYSQL_ROOT_PASSWORD=secret \
    -e MYSQL_DATABASE=todos \


You’ll notice we’re using a volume named todo-mysql-data here and mounting it at /var/lib/mysql, which is where MySQL stores its data. However, we never ran a docker volume create command. Docker recognizes we want to use a named volume and creates one automatically for us.

3- confirm the database is up and running:

docker exec -it <mysql-container-id> mysql -p

Sometimes it’s useful to start with a clean slate and remove all Docker containers and even images. Here are some handy shortcuts.

List all containers (only IDs)

$docker ps -aq

Stop all running containers

$docker stop $(docker ps -aq)

Remove all containers

$docker rm $(docker ps -aq)

Remove all images

$docker rmi $(docker images -q)

Dockerize a node app

What is argument[0] used for in Selenium code?

argument[0] is used in javascript function to pass on the value of the WebElement.


WebElement webElement = driver.findElement(By.xpath("xpath_element"));
JavascriptExecutor javaScriptExecutor = (JavascriptExecutor)driver;
javaScriptExecutor.executeScript("arguments[0].click()", webElement);

What is the @ sign in java used for?

The @ symbol denotes a Java Annotation. What a Java annotation does, is that it adds a special attribute to the variable, method, class, interface, or other language elements.

“In the Java computer programming language, an annotation is a form of syntactic metadata that can be added to Java source code. “

Github cheatsheet

Getting started:

1. Installing Git

sudo apt-get install git

2. Configuring Git

$ git config --global "My Name"

3. Creating a new repository - git init

$ cd Desktop/git_exercise/

4. Checking the status - git status

$ git status

5. Staging

$ git add hello.txt


$ git add -A

equivalent to

$ git add .

6. Commiting

$ git commit -m "Initial commit."

7. Modify the last commit message:

$ git --amend

Start your Git repo anew

To remove the git file and create anew in the repo:

cd /path/to/your/repo
rm -rf .git
git init

Add a remote repository

In general:

$ git remote add origin

Push to remote:

If it’s a commit on the master branch:

$ git push origin master

If it’s a commit on some branch named “some-branch”:

$ git push origin some-branch

Pull request

In our workflow we shall send code to CR (code review) before it goes to QA.

Create a branch

For that you create a branch, then push the code to your branch and the pull request is done in the master branch dashboard.

$ git branch some-feature 
$ git checkout some-feature

You can create the branch and go in the branch in command:

$ git checkout -b some-feature

# Edit some code

$ git commit -a -m "Add first draft of some feature"
$ git push origin some-branch

“After Bitbucket has her feature branch, Mary can create the pull request through her Bitbucket account by navigating to her forked repository and” clicking on Pull requests in the side bar and then “clicking the Pull request button in the top-right corner.“


More reading:

Set gitignore

touch ~/.gitignore
git config --global core.excludesFile ~/.gitignore
sudo vim ~/.gitignore

edit file with:


to exclude all files ending with

for a local approach simply create and edit the .gitignore file in the affected local repository.

If the file has already been staged, remove it by using:

$ git restore --staged <file>.

All those worked:


the directory tree was:






If you accidentally sync and can’t push anymore:

hint: Updates were rejected because the tip of your current branch is behind
hint: its remote counterpart. Integrate the remote changes (e.g.
hint: 'git pull ...') before pushing again.
hint: See the 'Note about fast-forwards' in 'git push --help' for details.

create a force push:

git push -f origin branchname

Set git Locally

cd in the folder were you want to clone the repo:

$ cd directory/you/clone
$ git init
$ git config “Your-Username” #can be different from your github username
$ git config “
$ ssh-keygen -t rsa -C “

Enter file in which to save the key (/home/username/.ssh/id_rsa): /home/username.ssh/id_rsa

copy the content of the in your github settings in your profile.

Set github local authentication to be able to clone and push:

List branches

List local branches

$git branch

List remote branches

$git branch -r

List all remote and local branches

$git branch -a

See what branch you are on:

$git status