# Prepare CentOS Server

This article describes how prepare a CentOS physical server to be added as a host to Platform9 Managed OpenStack (PMO) cloud.

{% hint style="info" %}
**Note**

For a description of PMO networking concepts, refer to the [Networking Basic Concepts tutorial](https://docs.platform9.com/managed-openstack/5.4/networks/networks-networking-concepts) [Networking](https://docs.platform9.com/managed-openstack/5.4/getting-started/generic-linux-kvm-setup/getting-started-configure-networking-kvm). Refer to [PMO prerequisites for Linux/KVM](https://docs.platform9.com/managed-openstack/5.4/getting-started/generic-linux-kvm-setup/getting-started-prerequisites-linux-kvm) for systems requirements and supported CentOS Operating System versions.
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### Supported Operating System Version

Platform9 Managed OpenStack supports CentOS 7+ (64-bit).

### Step 1 - Install CentOS Operating System

Make sure that your server is configured appropriately with access to storage and physical networking. Download and install CentOS on your physical server. You can download CentOS distributions from here: <http://wiki.centos.org/Download>

{% hint style="info" %}
**Note**

We recommend installing the minimal CentOS operating system. Platform9 agents are prepared to pull in any required package dependencies and get them installed on your server to prepare it to be part of OpenStack. This includes any libvirt/KVM package dependencies.
{% endhint %}

It’s usually a good practice to get your system up to date with regard to the latest patches and updates.

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```bash
sudo yum -y update
```

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### Step 2 - Ensure Virtualization is Enabled

Ensure that virtualization is enabled for your server by checking your server’s BIOS settings. If disabled, enable virtualization for the server to be able to act as a hypervisor within Platform9 Managed OpenStack.

### Step 3 - Ensure the System Clock is Synchronized

Your host will fail to authenticate with Platform 9 services if its date / time settings are incorrect. Type `date` to verify that the current date and time are correct. If they aren’t, then one possible fix is to enable the network time protocol daemon service:

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{% tab title="Bash" %}

```bash
sudo yum -y install ntp
chkconfig --add ntpd
service ntpd start
```

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The following image (Figure 1) represents three hypervisors connected in a Managed OpenStack Neutron network.

<figure><img src="https://1126553421-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FZ8EciOmTwpkZCkUOCYd9%2Fuploads%2Fgit-blob-6d3860f81348271643c6d15b91385adb1b8ac0a9%2F1604966594.png?alt=media" alt=""><figcaption></figcaption></figure>

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**Note**

There are no separate network nodes in a Distributed Virtual Routing (DVR) network.
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### Step 4 - Set SELinux to permissive

This is required for Open vSwitch (OVS) to be able to manage networking.

Run the following commands to set SELinux to permissive.

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```bash
sed -i s/SELINUX=enforcing/SELINUX=permissive/g /etc/selinux/config
setenforce 0
```

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### Step 5 - Disable Firewalld and NetworkManager

This is required for KVM and OVS to be able to create iptables rules directly without firewalld getting in the way.

Run the following commands to disable firewalld and NetworkManager.

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```bash
systemctl disable firewalld
  systemctl stop firewalld
  systemctl disable NetworkManager
  systemctl stop NetworkManager
```

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### Step 6 - Enable Network

Run the following command to enable network.

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```bash
systemctl enable network
```

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### Step 7 - Load the modules needed for Neutron

Run the following commands to load the modules needed for Neutron.

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{% tab title="Bash" %}

```bash
modprobe bridge
  modprobe 8021q
  modprobe bonding
  modprobe tun
  modprobe br_netfilter
  echo bridge > /etc/modules-load.d/pf9.conf
  echo 8021q >> /etc/modules-load.d/pf9.conf
  echo bonding >> /etc/modules-load.d/pf9.conf
  echo tun >> /etc/modules-load.d/pf9.conf
  echo br_netfilter >> /etc/modules-load.d/pf9.conf
```

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### Step 8 - Add sysctl options

Run the following commands to add sysctl options.

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{% tab title="Bash" %}

```bash
echo net.ipv4.conf.all.rp_filter=0 >> /etc/sysctl.conf
  echo net.ipv4.conf.default.rp_filter=0 >> /etc/sysctl.conf
  echo net.bridge.bridge-nf-call-iptables=1 >> /etc/sysctl.conf
  echo net.ipv4.ip_forward=1 >> /etc/sysctl.conf
  echo net.ipv4.tcp_mtu_probing=2 >> /etc/sysctl.conf
  sysctl -p
```

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### Step 9 - Add the Platform9 YUM Repo

Run the following command to install the Platform9 YUM repository.

For Platform9 releases upto and including 4.4:

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```bash
yum -y install https://s3-us-west-1.amazonaws.com/platform9-neutron/noarch/platform9-neutron-repo-1-0.noarch.rpm
```

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### Step 10 - Install Open vSwitch

Run the following command to get a list of available Open vSwitch versions.

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```bash
yum --showduplicates list openvswitch
```

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If you wish to install an available older version, run the following command.

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```bash
yum install openvswitch-<version>
```

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Alternatively, if you wish to install the latest version, run the following command.

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```bash
yum install openvswitch
```

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### Step 11 - Enable and start Open vSwitch

Run the following commands to enable and start Open vSwitch.

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```bash
systemctl enable openvswitch
systemctl start openvswitch
```

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### Step 12 - Install QEMU KVM EV

Run the following commands to install QEMU KVM EV

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```bash
yum install centos-release-qemu-ev
yum install qemu-kvm-ev
```

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### Step 13 - Install Router Advertisement Daemon

Run the following command to install radvd

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```bash
yum -y install radvd
```

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### Step 14 - Configure physical interfaces

{% hint style="info" %}
**Info**

Figure 1 in the article represents a sample Neutron network configuration. Steps 10 through 14 are based on the configuration shown in Figure 1 from the article. Steps 10 through 14 describe the configuration of physical interfaces into a Linux bond, addition of VLAN interfaces for management, VXLAN/GRE network traffic and storage. You may or may not require one or more of these steps. The steps to follow would be based on your Neutron network configuration. For instance, if you do not plan on using VXLAN/GRE, you can skip the step to set up VXLAN/GRE tunneling interface.
{% endhint %}

We assume the interface names to be eth0 and eth1.

Substitute eth0 and eth1 with the appropriate interface names per your setup, when you run the commands given for this step.

Similarly, we are assuming an MTU of 9000 - VXLAN requires an MTU of at least 1600.

Make sure all physical switches are configured to handle the MTU of 1600 or you might have problems.

Run the following commands to configure physical interfaces.

**/etc/sysconfig/network-scripts/ifcfg-eth0**

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```bash
DEVICE=eth0
  ONBOOT=yes
  BOOTPROTO=none
  MTU=9000
  MASTER=bond0
  SLAVE=yes
```

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**/etc/sysconfig/network-scripts/ifcfg-eth1**

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```bash
DEVICE=eth1
  ONBOOT=yes
  BOOTPROTO=none
  MTU=9000
  MASTER=bond0
  SLAVE=yes
```

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### Step 15 - Set up the Bond interface

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**Note**

We are assuming bonding type=4 (LACP) refer to CentOS [Bonding Types](https://wiki.centos.org/TipsAndTricks/BondingInterfaces) to learn more.
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Run the following commands to set up the bond interface.

**/etc/sysconfig/network-scripts/ifcfg-bond0**

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```bash
DEVICE=bond0
  ONBOOT=yes
  BONDING_MASTER=yes
  BONDING_OPTS="mode=4"
  MTU=9000
```

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### Step 16 - Setup the Management interface

{% hint style="info" %}
**Note**

We are assuming VLAN 101 for the Management network. Replace it with the correct VLAN ID per your setup. We are assuming subnet 192.0.2.0/24 for Management. Replace it with the correct subnet per your setup.
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**/etc/sysconfig/network-scripts/ifcfg-bond0.101**

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```bash
DEVICE=bond0.101
  ONBOOT=yes
  BOOTPROTO=none
  TYPE=Vlan
  VLAN=yes
  IPADDR=192.0.2.10
  NETMASK=255.255.255.0
  GATEWAY=192.0.2.1
  DNS1=192.0.2.100
  DNS2=192.0.2.200
```

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### Step 17 - Setup the VXLAN/GRE tunneling interface (Optional)

{% hint style="info" %}
**Note**

We are assuming VLAN 102 for VXLAN/GRE tunneling. Please use the correct VLAN per your setup. We are assuming subnet 198.51.100.0/24 for VXLAN/GRE tunneling. Please use the correct subnet per your setup.
{% endhint %}

Run the following commands to VXLAN/GRE tunneling interface.

**/etc/sysconfig/network-scripts/ifcfg-bond0.102**

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```bash
DEVICE=bond0.102
  ONBOOT=yes
  BOOTPROTO=none
  TYPE=Vlan
  VLAN=yes
  IPADDR=198.51.100.10
  NETMASK=255.255.255.0
```

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### Step 18 - Setup the Storage interface (Optional)

{% hint style="info" %}
**Note**

We are assuming VLAN 103 for the storage network. Replace it with the VLAN per your setup. We are assuming subnet 203.0.113.0/24 for the storage network. Replace it with the subnet per your setup.
{% endhint %}

Run the following commands to set up the storage interface.

**/etc/sysconfig/network-scripts/ifcfg-bond0.103**

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{% tab title="Bash" %}

```bash
DEVICE=bond0.103
  ONBOOT=yes
  BOOTPROTO=none
  TYPE=Vlan
  VLAN=yes
  IPADDR=203.0.113.10
  NETMASK=255.255.255.0
```

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### Step 19 - Restart Networking

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**Warning**

Make sure you have console access to your host. You will be disconnected if the configuration is incorrect.
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Run the following command to restart the network service.

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```bash
systemctl restart network.service
```

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### Step 20 - Create OVS Bridges

The number of OVS bridges you need will determine on how many physical networks your hosts connect to, and what types of networks you will be creating.

Let us look at some basic networking terminology before creating the bridges.

* An **access port** represents a single flat physical network or VLAN, and will carry untagged traffic.
* A **trunk port** logically groups together multiple VLANs. An 802.1Q QTag header will be inserted into the Ethernet frame for all VLAN traffic. All untagged traffic is implicitly assigned a default, native VLAN per your data center’s switch configuration.

Each physical network corresponds to a trunk or access port (an individual NIC, or a pair of NICs bonded together) on the host. An Open vSwitch bridge must be created for each physical network.

When configuring Platform9 OpenStack’s Networking Config, each physical network is given a Label as a name, and that label mapped to a particular OVS bridge on the host during host authorization.

Let us look at two different examples of common host networking setups.

### Example 1: Non-DVR setup with one external flat network, and trunk port for VLAN traffic

The following figure (Figure 2) represents a non-DVR network setup with an external flat network, and a trunk port for VLAN traffic.

<figure><img src="https://1126553421-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FZ8EciOmTwpkZCkUOCYd9%2Fuploads%2Fgit-blob-66e66d8898939eb9f6fb2cea310f2ec235a824e7%2F1604967341.jpg?alt=media" alt=""><figcaption></figcaption></figure>

In the above figure 2, the network has a trunk port consisting of eth0 and eth1 in a bond that will carry our VLAN based networks(tenant, provider), as well as a dedicated port (eth2) that connects to a separate external network. This is a legacy, non-DVR setup where external connectivity and L3 capability is only on network nodes. Nodes that are hypervisors only carry the tenant network traffic, and need just 1 OVS bridge.

Run the following commands to add OVS bridges on the hypervisors. The steps below assume eth0/eth1 have already been configured in a Linux bond called *bond0*. Please refer to steps 10-15 to set up your physical interfaces.

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```bash
ovs-vsctl add-br br-vlan
ovs-vsctl add-port br-vlan bond0
```

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On our network node, we have a separate NIC that connects to a different physical network. For this, we need a separate OVS bridge.

Run the following commands to add an OVS bridge.

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```bash
ovs-vsctl add-br br-ext
ovs-vsctl add-port br-ext eth2
```

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### Example 2: DVR setup with a pair of NICs in a bond

The following figure (Figure 3) represents a DVR network setup with a pair of NICs in a bond.

<figure><img src="https://1126553421-files.gitbook.io/~/files/v0/b/gitbook-x-prod.appspot.com/o/spaces%2FZ8EciOmTwpkZCkUOCYd9%2Fuploads%2Fgit-blob-6773c070db0b5ea7f97faed98900b71d68f65c80%2F1604967435.jpg?alt=media" alt=""><figcaption></figcaption></figure>

In the DVR setup seen in figure 3 above, every host has external L3 connectivity. Here, we only have a pair of NICs in a bond. Therefore this OVS Bridge can only support one Flat (untagged) network, and as many VLAN-tagged networks as your networking infrastructure allows. There are multiple external networks that are VLAN-based, in addition to our tenant networks.

Run the following commands to add an OVS bridge on all hosts.

{% hint style="info" %}
**Note**

The steps below assume eth0/eth1 have already been configured in a Linux bond called “bond0”. Refer to steps 10-14 to set up your physical interfaces.
{% endhint %}

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```bash
ovs-vsctl add-br br-vlan
ovs-vsctl add-port br-vlan bond0
```

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At this point your CentOS server is ready to be added as a hypervisor to Platform9 Managed OpenStack (PMO).