IP Reserved Loopback and Private Addresses

Range Start Address	Range End Address	“Classful” Address Equivalent	Classless Address Equivalent	Description
0.0.0.0	0.255.255.255	Class A network 0.x.x.x	0/8	Reserved.
10.0.0.0	10.255.255.255	Class A network 10.x.x.x	10/8	Class A private address block.
127.0.0.0	127.255.255.255	Class A network 127.x.x.x	127/8	Loopback address block.
128.0.0.0	128.0.255.255	Class B network 128.0.x.x	128.0/16	Reserved.
169.254.0.0	169.254.255.255	Class B network 169.254.x.x	169.254/16	Class B private address block reserved for automatic private address allocation. See the section on DHCP for details.
172.16.0.0	172.31.255.255	16 contiguous Class B networks from 172.16.x.x through 172.31.x.x	172.16/12	Class B private address blocks.
191.255.0.0	191.255.255.255	Class B network 191.255.x.x	191.255/16	Reserved.
192.0.0.0	192.0.0.255	Class C network 192.0.0.x	192.0.0/24	Reserved.
192.168.0.0	192.168.255.255	256 contiguous Class C networks from 192.168.0.x through 192.168.255.x	192.168/16	Class C private address blocks.
223.255.255.0	223.255.255.255	Class C network 223.255.255.x	223.255.255/24	Reserved.

Linux Firewall for Docker Swarm on CentOS 7

Firewalld

firewall-cmd --add-port=2376/tcp --permanent
firewall-cmd --add-port=2377/tcp --permanent
firewall-cmd --add-port=7946/tcp --permanent
firewall-cmd --add-port=7946/udp --permanent
firewall-cmd --add-port=4789/udp --permanent
firewall-cmd --reload
systemctl restart docker

Docker ENTRYPOINT vs CMD

Both ENTRYPOINT and CMD can identify which executable should be run when a container is started from image.

Docker block oubound network traffic

Install iptables in docker and run it in entrypoint.sh. To disable iptables, run touch myenv/MAINTENANCE and restart container

Do not display last username on logon screen in Windows

Using Group Policy

GlusterFS

commands

sudo yum install centos-release-gluster312.noarch
sudo yum install glusterfs gluster-cli glusterfs-libs glusterfs-server
sudo mkdir /home/glusterfs
sudo chown <user>:<user group> /home/glusterfs
sudo gluster peer probe swarm-manager01.yourdomain.com
sudo service enable gluster.service
sudo systemctl enable gluster.service
sudo systemctl enable glusterd.service
sudo systemctl start glusterd
sudo systemctl status glusterd
sudo systemctl enable glusterd.service
sudo systemctl start glusterd.service
sudo gluster peer probe swarm-manager02.yourdomain.com
sudo gluster peer probe swarm-manager03.yourdomain.com
sudo gluster peer probe swarm-manager01.yourdomain.com
sudo gluster peer probe swarm-node01.yourdomain.com
sudo gluster peer probe swarm-node02.yourdomain.com
sudo gluster peer probe swarm-worker02.yourdomain.com
sudo gluster peer probe swarm-worker01.yourdomain.com
sudo gluster peer status
gluster volume create gfs replica 3 swarm-manager01.yourdomain.com:/home/glusterfs swarm-manager02.yourdomain.com:/home/glusterfs swarm-worker01.yourdomain.com:/home/glusterfs gluster volume create gfs replica 5 swarm-manager01.yourdomain.com:/home/glusterfs swarm-manager02.yourdomain.com:/home/glusterfs swarm-worker01.yourdomain.com:/home/glusterfs \
sudo gluster volume create gfs replica 5 swarm-manager01.yourdomain.com:/home/glusterfs swarm-manager02.yourdomain.com:/home/glusterfs swarm-worker01.yourdomain.com:/home/glusterfs swarm-worker02.yourdomain.com:/home/glusterfs
sudo gluster volume create gfs replica 3 swarm-manager01.yourdomain.com:/home/glusterfs swarm-manager02.yourdomain.com:/home/glusterfs swarm-worker01.yourdomain.com:/home/glusterfs swarm-worker02.yourdomain.com:/home/glusterfs
sudo gluster volume create gfs replica 5 swarm-manager03.yourdomain.com/home/glusterfs swarm-manager01.yourdomain.com:/home/glusterfs swarm-manager02.yourdomain.com:/home/glusterfs swarm-worker01.yourdomain.com:/home/glusterfs swarm-worker02.yourdomain.com:/home/glusterfs
mkdir -p /home/glusterfs/1/brick
sudo gluster volume create gfs replica 5 swarm-manager03.yourdomain.com/home/glusterfs/1/brick swarm-manager01.yourdomain.com:/home/glusterfs/3/brick swarm-manager02.yourdomain.com:/home/glusterfs/2/brick swarm-worker01.yourdomain.com:/home/glusterfs/4/brick swarm-worker02.yourdomain.com:/home/glusterfs/brick
sudo gluster volume create gfs replica 5 swarm-manager03.yourdomain.com:/home/glusterfs/1/brick swarm-manager01.yourdomain.com:/home/glusterfs/3/brick swarm-manager02.yourdomain.com:/home/glusterfs/2/brick swarm-worker01.yourdomain.com:/home/glusterfs/4/brick swarm-worker02.yourdomain.com:/home/glusterfs/brick
sudo gluster volume create gfs replica 5 swarm-manager03.yourdomain.com:/home/glusterfs/1/brick swarm-manager01.yourdomain.com:/home/glusterfs/3/brick swarm-manager02.yourdomain.com:/home/glusterfs/2/brick swarm-worker01.yourdomain.com:/home/glusterfs/4/brick swarm-worker02.yourdomain.com:/home/glusterfs/brick
sudo gluster volume create gfs replica 5 swarm-manager03.yourdomain.com:/home/glusterfs/1/brick swarm-manager01.yourdomain.com:/home/glusterfs/3/brick swarm-manager02.yourdomain.com:/home/glusterfs/2/brick swarm-worker01.yourdomain.com:/home/glusterfs/4/brick swarm-worker02.yourdomain.com:/home/glusterfs/brick force
sudo gluster list
sudo gluster volume list
sudo gluster start gfs
sudo gluster volume start gfs
sudo gluster volume status gfs

Guacamole, RDP, Windows 10 and Windows Server 2016

Currently, Guacamole cannot support RDP for Windows 10 and Windows Server 2016. We can change RDP settings on Windows 10/Server 2016 to make it works.

Apache Proxy Balancer

Enable proxy models

sudo a2enmod proxy_html
sudo a2enmod proxy_http
sudo a2enmod proxy_wstunnel
sudo a2enmod proxy_ajp
sudo a2enmod lbmethod_byrequests
sudo a2enmod lbmethod_bytraffic
sudo a2enmod lbmethod_bybusyness
sudo a2enmod lbmethod_heartbeat

Create a MongoDB Replica Set

Create 3 mongodb servers. Make sure update hosts files on all nodes or on DNS server

168.1.10 mongodb01
168.1.11 mongodb02
168.1.12 mongodb03

semanage Command not Found in CentOS 7

If you can’t find a command in CentOS, try the following example (for command semanage):

sudo yum provides /usr/sbin/semanage

Then install the package which needs.