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Linux Challenge 2

The app server called centos-host is running a Go app on the 8081 port. You have been asked to troubleshoot some issues with yum/dnf on this system, Install Nginx server, configure Nginx as a reverse proxy for this Go app, install firewalld package and then configure some firewall rules.

All the tasks require you to be root, so the first step is to become root

sudo -i

Individual Steps

Centos Host

Here we are required to diagnose why yum is not working, and fix it. This has to be done before we can do anything else!

The error we get if we try to use yum to install a package indicates something is up with DNS resolution, to the first place to look is resolv.conf

We note that there are no name servers defined, therefore this is the reason why nothing can be resolved.

Fix DNS resolution 
vi /etc/resolv.conf

Add Google nameserver as the first line in the file and save

nameserver 8.8.8.8

Packages

Install "nginx" package 
yum install -y nginx
Install "firewalld" package 
yum install -y firewalld

Security

Start and Enable "firewalld" service. 
systemctl enable firewalld
systemctl start firewalld

Add firewall rules to allow only incoming port "22", "80" and "8081" The firewall rules must be permanent and effective immediately.

Add firewall rules, make permanent and effective. 
firewall-cmd --zone=public --add-port=80/tcp --permanent
firewall-cmd --zone=public --add-port=8081/tcp --permanent
firewall-cmd --zone=public --add-port=22/tcp --permanent
firewall-cmd --reload

Go App

Start GoApp by running the "nohup go run main.go &" command from "/home/bob/go-app/" directory

Run the go app.

pushd /home/bob/go-app
nohup go run main.go &
popd

Although the command prompt will return immediately because the process has been started as a background task, it will take 2-3 minutes before it is actually running due to the time it takes to compile. While that is happening, do the nginx configuration.

Nginx

Configure Nginx as a reverse proxy for the GoApp so that we can access the GoApp on port "80"

The GoApp itself is listening on port 8081. By configuring nginx as a reverse proxy listening on port 80 we can redirect the port 80 request somwhere else, in this case on the same machine but on port 8081.

vi /etc/nginx/nginx.conf

We need to create a new location stanza for the root path within the server { stanza and redirect anything arriving there to the go app which is running on http://localhost:8081. For this we use a proxy_pass directive within the location stanza.

The existing server stanza looks like this

    server {
        listen       80;
        listen       [::]:80;
        server_name  _;
        root         /usr/share/nginx/html;

        # Load configuration files for the default server block.
        include /etc/nginx/default.d/*.conf;

        error_page 404 /404.html;
        location = /404.html {
        }

        error_page 500 502 503 504 /50x.html;
        location = /50x.html {
        }
    }

Within this, insert the new location stanza so it looks like this

    server {
        listen       80;
        listen       [::]:80;
        server_name  _;
        root         /usr/share/nginx/html;

        # Load configuration files for the default server block.
        include /etc/nginx/default.d/*.conf;

        location = / {
            proxy_pass  http://localhost:8081;
        }

        error_page 404 /404.html;
        location = /404.html {
        }

        error_page 500 502 503 504 /50x.html;
        location = /50x.html {
        }
    }
Start and Enable "nginx" service 
systemctl enable nginx
systemctl start nginx

bob

Click the GoApp button above the terminal. You should get a login screen.

Automate the entire lab in a single script!

Pretty much everything done above, in the same order. We automate the vi steps by using sed to do the insertions into resolv.conf and nginx.conf and we automate Bob's login using curl

Single Script Automation

First, become root

sudo -i

Then

{
# Paste this entire script to the command prompt.
# When it completes, press the check button.

#################################
#
# Centos Host
#
#################################

## Fix yum DNS errors by inserting google nameserver
# Can't use sed -i here as we get "Device or resource busy"
sed '1inameserver 8.8.8.8' /etc/resolv.conf > /tmp/resolv.conf
# Can't use cp or mv for the same reason
cat  /tmp/resolv.conf > /etc/resolv.conf

#################################
#
# Packages
#
#################################

yum install -y nginx firewalld

#################################
#
# Security
#
#################################

# Start and Enable "firewalld" service.
systemctl enable firewalld
systemctl start firewalld
# Add firewall rules to allow only incoming port "22", "80" and "8081" and make permanent
firewall-cmd --zone=public --add-port=80/tcp --permanent
firewall-cmd --zone=public --add-port=8081/tcp --permanent
firewall-cmd --zone=public --add-port=22/tcp --permanent
firewall-cmd --reload

#################################
#
# GoApp
#
#################################

# Compile and run go-app from "/home/bob/go-app/" directory
# Do the compile in the foreground so as not to have to poll a background task for completion
pushd /home/bob/go-app
go build -o go-app .
nohup ./go-app &

popd

#################################
#
# Nginx
#
#################################

# Configure Nginx as a reverse proxy for the GoApp so that we can access the GoApp on port "80"
# Do this by inserting a location stanza for root path at line 47 specifying the proxy pass to the go app
sed -i '47i\        location / {\n\            proxy_pass  http://localhost:8081;\n        }\n' /etc/nginx/nginx.conf

# Start nginx
systemctl enable nginx
systemctl start nginx

#################################
#
# bob
#
#################################

# bob is able to login into GoApp using username "test" and password "test"
if curl -s -u test:test http://localhost:80 > /dev/null
then
    echo
    echo "Success! Bob logged in!"
    echo "Press 'Check' button to complete lab"
else
    echo
    echo "Bob cannot log in!"
fi
}