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Chapter 2. Using a firewall

Firewalls are not required in Red Hat build of MicroShift, but using a firewall can prevent undesired access to the Red Hat build of MicroShift API.

2.1. About network traffic through the firewall
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Firewalld is a networking service that runs in the background and responds to connection requests, creating a dynamic customizable host-based firewall. If you are using Red Hat Enterprise Linux (RHEL) for Edge with Red Hat build of MicroShift, firewalld should already be installed and you just need to configure it. Details are provided in procedures that follow. Overall, you must explicitly allow the following OVN-Kubernetes traffic when the firewalld service is running:

CNI pod to CNI pod
CNI pod to Host-Network pod Host-Network pod to Host-Network pod
CNI pod
The Kubernetes pod that uses the CNI network
Host-Network pod
The Kubernetes pod that uses host network You can configure the firewalld service by using the following procedures. In most cases, firewalld is part of {rhel} installations. If you do not have firewalld, you can install it with the simple procedure in this section.
Important

Red Hat build of MicroShift pods must have access to the internal CoreDNS component and API servers.

2.2. Installing the firewalld service
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If you are using RHEL for Edge, firewalld should be installed. To use the service, you can simply configure it. The following procedure can be used if you do not have firewalld, but want to use it.

Install and run the firewalld service for Red Hat build of MicroShift by using the following steps.

Procedure

  1. Optional: Check for firewalld on your system by running the following command: 

    $ rpm -q firewalld
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  2. If the firewalld service is not installed, run the following command: 

    $ sudo dnf install -y firewalld
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  3. To start the firewall, run the following command: 

    $ sudo systemctl enable firewalld --now
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2.3. Required firewall settings
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An IP address range for the cluster network must be enabled during firewall configuration. You can use the default values or customize the IP address range. If you choose to customize the cluster network IP address range from the default 10.42.0.0/16 setting, you must also use the same custom range in the firewall configuration.

Expand
Table 2.1. Firewall IP address settings
IP RangeFirewall rule requiredDescription

10.42.0.0/16

No

Host network pod access to other pods

169.254.169.1

Yes

Host network pod access to Red Hat build of MicroShift API server

The following are examples of commands for settings that are mandatory for firewall configuration:

Example commands

  • Configure host network pod access to other pods: 

    $ sudo firewall-cmd --permanent --zone=trusted --add-source=10.42.0.0/16
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  • Configure host network pod access to services backed by Host endpoints, such as the Red Hat build of MicroShift API: 

    $ sudo firewall-cmd --permanent --zone=trusted --add-source=169.254.169.1
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2.4. Using optional port settings
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The Red Hat build of MicroShift firewall service allows optional port settings.

Procedure

  • To add customized ports to your firewall configuration, use the following command syntax: 

    $ sudo firewall-cmd --permanent --zone=public --add-port=<port number>/<port protocol>
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    Expand
    Table 2.2. Optional ports
    Port(s)Protocol(s)Description

    80

    TCP

    HTTP port used to serve applications through the OpenShift Container Platform router.

    443

    TCP

    HTTPS port used to serve applications through the OpenShift Container Platform router.

    5353

    UDP

    mDNS service to respond for OpenShift Container Platform route mDNS hosts.

    30000-32767

    TCP

    Port range reserved for NodePort services; can be used to expose applications on the LAN.

    30000-32767

    UDP

    Port range reserved for NodePort services; can be used to expose applications on the LAN.

    6443

    TCP

    HTTPS API port for the Red Hat build of MicroShift API.

The following are examples of commands used when requiring external access through the firewall to services running on Red Hat build of MicroShift, such as port 6443 for the API server, for example, ports 80 and 443 for applications exposed through the router.

Example commands

  • Configuring a port for the Red Hat build of MicroShift API server: 

    $ sudo firewall-cmd --permanent --zone=public --add-port=6443/tcp
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  • Configuring ports for applications exposed through the router: 

    $ sudo firewall-cmd --permanent --zone=public --add-port=80/tcp
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    $ sudo firewall-cmd --permanent --zone=public --add-port=443/tcp
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2.5. Allowing network traffic through the firewall
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You can allow network traffic through the firewall by configuring the IP address range and inserting the DNS server to allow internal traffic from pods through the network gateway.

Procedure

  1. Use one of the following commands to set the IP address range:

    1. Configure the IP address range with default values by running the following command: 

      $ sudo firewall-offline-cmd --permanent --zone=trusted --add-source=10.42.0.0/16
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    2. Configure the IP address range with custom values by running the following command: 

      $ sudo firewall-offline-cmd --permanent --zone=trusted --add-source=<custom IP range>
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  2. To allow internal traffic from pods through the network gateway, run the following command: 

    $ sudo firewall-offline-cmd --permanent --zone=trusted --add-source=169.254.169.1
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2.5.1. Applying firewall settings
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To apply firewall settings, use the following one-step procedure:

Procedure

  • After you have finished configuring network access through the firewall, run the following command to restart the firewall and apply the settings: 
$ sudo firewall-cmd --reload
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2.6. Verifying firewall settings
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After you have restarted the firewall, you can verify your settings by listing them.

Procedure

  • To verify rules added in the default public zone, such as ports-related rules, run the following command: 

    $ sudo firewall-cmd --list-all
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  • To verify rules added in the trusted zone, such as IP-range related rules, run the following command: 

    $ sudo firewall-cmd --zone=trusted --list-all
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2.7. Known firewall issue
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  • To avoid breaking traffic flows with a firewall reload or restart, execute firewall commands before starting Red Hat build of MicroShift. The CNI driver in Red Hat build of MicroShift makes use of iptable rules for some traffic flows, such as those using the NodePort service. The iptable rules are generated and inserted by the CNI driver, but are deleted when the firewall reloads or restarts. The absence of the iptable rules breaks traffic flows. If firewall commands have to be executed after Red Hat build of MicroShift is running, manually restart ovnkube-master pod in the openshift-ovn-kubernetes namespace to reset the rules controlled by the CNI driver.
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