Most Used Docker Commands:Interview Question
Pre-Requisite:
What is PostgreSQL?
PostgreSQL has object-oriented features for handling unstructured data, it is widely used as a Relational Database.
PostgreSQL supports both SQL and JSON to implement relational and non-relational queries on data present inside databases. In other words, with PostgreSQL, you can write SQL commands to process data present in tables that belong to the respective database servers. Because of its vast features and functionalities, PostgreSQL is reportedly ranked 4th among the most popular databases worldwide.
Install PostgreSQL on Docker
Assuming there is no Docker image that suits your needs in the Docker Hub, you can create one yourself.
Start by creating a new Dockerfile:
Note: This PostgreSQL setup is for development-only purposes. Refer to the PostgreSQL documentation to fine-tune these settings so that they are suitably secure.
If you want to use the above code kindly download it from below github repository:
https://github.com/sidharth8891/dockerhelp/blob/main/dockerFilePostgreSql
Build an image from the Dockerfile and assign it a name.
$ docker build -t eg_postgresql .
Run the PostgreSQL server container (in the foreground):
$ docker run --rm -P --name pg_test eg_postgresql
There are two ways to connect to the PostgreSQL server. You can use Link Containers, or we can access it from our host (or the network).
Note: The
--rmremoves the container and its image when the container exits successfully.
Use container linking
Containers can be linked to another container’s ports directly used --link remote_name:local_alias in the client’s docker run. This sets up a number of environmental variables that can then be used to connect:
$ docker run --rm -t -i --link pg_test:pg eg_postgresql bash
postgres@7ef98b1b7243:/$ psql -h $PG_PORT_5432_TCP_ADDR -p $PG_PORT_5432_TCP_PORT -d docker -U docker --password
**********
Connect from your host system
Assuming you have the postgresql-client installed, you can use the host-mapped port to test it as well. You need to use docker ps this to find out what local host port the container is mapped to first:
$ docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
5e24362f27f6 eg_postgresql:latest /usr/lib/postgresql/ About an hour ago Up About an hour 0.0.0.0:49153->5432/tcp pg_test
$ psql -h localhost -p 49153 -d docker -U docker --password
Test the database
Once you have authenticated and have a docker =# prompt, you can create a table and populate it.
If you want to use the above code, kindly download it from the below github link:
https://github.com/sidharth8891/dockerhelp/blob/main/TestTheDatabase
Use container volumes
You can use the defined volumes to inspect the PostgreSQL log files and to backup your configuration and data:
$ docker run --rm --volumes-from pg_test -t -i busybox sh
/ # ls
bin etc lib linuxrc mnt proc run sys usr
dev home lib64 media opt root sbin tmp var
/ # ls /etc/postgresql/9.3/main/
environment pg_hba.conf postgresql.conf
pg_ctl.conf pg_ident.conf start.conf
/tmp # ls /var/log
ldconfig postgresqlInterview questions for SDET/Automation Testing: Top 21 GIT interview questions Top 30 Selenium Webdriver Interview Q&A
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