System Administration

Before diving into creating cloud applications, it is necessary that you understand a bit about system administration, specifically package and service management. The instructions are given below for Ubuntu 18.04 and CentOS 7. Choose the operating system with which you’re most comfortable, although it is useful to look through the information for both systems.

Ubuntu 18.04

Super User

System administration commands must be run from the “root” (super user) account.

Normally with Ubuntu, you will log into the “ubuntu” account, which is a normal user account, not a super user account. To run system administration commands from the “ubuntu” account, there are two options:

• Prefix each command with sudo. This command will switch temporarily to the super user account and execute the command given to sudo.

• Switch into the “root” account with the command “sudo su -“. This creates a new session with the “root” account. System administrator accounts can be run with a sudo prefix. To close the “root” shell and return to the “ubuntu” account, just type exit.

On Exoscale, there is also a third option. The Exoscale Ubuntu images are configured so that you can SSH directly into the root account. Just change the command: ssh ubuntu@ipv4-address to ssh root@ipv4-address.

Package Management

Try all of these command to understand how they work. Try searching, installing, and removing the “nginx” package. Nginx is one of the standard web servers.

Editors

To administer services on a virtual machine, you will need to be able to edit configuration files. The editors that are installed by default on Ubuntu 18.04 are: nano and vi. You need to be familiar with one of them. If you’re not already familiar with vi, choose nano. It has a very short learning curve. You can also install emacs (package name “emacs-nox”) if you’re familiar with it.

Service Management

Services are normally managed with the systemctl command (and friends). The full service management subsystem is called systemd. Earlier Ubuntu operating systems used a different system management system.

To understand how these commands work, reinstall the “nginx” package. When the service is started, you should be able to see the default landing page with the command:

curl http://localhost

This will dump the raw HTML content. In the HTML, you should see a header element like <h1>Welcome to nginx!</h1>.

Try to do the same from outside of the machine. It will likely fail because the server cannot be contacted from your browser. There are probably two reasons why. Can you think of what they could be?

The first reason is probably that your default security group on Exoscale is not configured correctly. We opened ports for ping and ssh, not for HTTP(S). Can you modify your default security group to open the ports 80 (HTTP) and 443 (HTTPS)?

The second reason is probably a local firewall running on your VM. The local firewall filters network traffic in addition to the security group. Rather than configuring both the security group and local firewall, it is generally easier just to disable the local firewall. The name of the local firewall service on Ubuntu is “ufw”. Can you use the system administrator commands to disable it?

IP Address

You will often need to find the IP address of your virtual machine. You can always get this from Exoscale, but it often easier to get this from within the VM itself. There are many ways to do this, but the easiest is just ifconfig. Look for the “inet” value assigned to the “eth0” interface.

CentOS 7

Super User

System administration commands must be run from the “root” (super user) account.

Normally with CentOS on Exoscale, you will log into the “centos” account, which is a normal user account, not a super user account. To run system administration commands from the “centos” account, there are two options:

• Prefix each command with sudo. This command will switch temporarily to the super user account and execute the command given to sudo.

• Switch into the “root” account with the command “sudo su -“. This creates a new session with the “root” account. System administrator accounts can be run with a sudo prefix. To close the “root” shell and return to the “centos” account, just type exit.

On Exoscale, there is also a third option. The Exoscale CentOS images are configured so that you can SSH directly into the root account. Just change the command: ssh centos@ipv4-address to ssh root@ipv4-address.

Package Management

The CentOS yum configuration only includes packages that are strictly part of the RedHat Enterprise Linux distribution. Many useful packages are in a separate package repository called EPEL.

To include the EPEL repository, install the package “epel-release”:

yum install epel-release

Unless you want to run a very minimal system, you will almost certainly want to systematically include the EPEL repository.

Try all of the package management commands to understand how they work. Try searching, installing, and removing the “nginx” package. Nginx is one of the standard web servers. The package for this is in EPEL, not the core CentOS repositories.

Editors

To administer services on a virtual machine, you will need to be able to edit configuration files. The vi editor is installed by default on CentOS 7.

If you’re not already familiar with vi, you may want to install nano. It has a very short learning curve. Just run yum install nano. You can also install emacs (package name “emacs-nox”) if you’re familiar with it.

Service Management

Services are normally managed with the systemctl command (and friends). The full service management subsystem is called systemd. Earlier CentOS operating systems used a different system management system.

To understand how these commands work, reinstall the “nginx” package. When the service is started, you should be able to see the default landing page with the command:

curl http://localhost

This will dump the raw HTML content. In the HTML, you should see a title element like <title>Test Page for the Nginx HTTP Server on Fedora</title>.

Try to do the same from outside of the machine. It will likely fail because the server cannot be contacted from your browser. There are probably two reasons why. Can you think of what they could be?

The first reason is probably that your default security group on Exoscale is not configured correctly. We opened ports for ping and ssh, not for HTTP(S). Can you modify your default security group to open the ports 80 (HTTP) and 443 (HTTPS)?

The second reason is probably a local firewall running on your VM. The local firewall filters network traffic in addition to the security group. Rather than configuring both the security group and local firewall, it is generally easier just to disable the local firewall. The name of the local firewall service on CentOS is “firewalld”. Can you use the system administrator commands to disable it?

IP Address

You will often need to find the IP address of your virtual machine. You can always get this from Exoscale, but it often easier to get this from within the VM itself. There are many ways to do this, but the easiest is just ifconfig. Look for the “inet” value assigned to the “eth0” interface.