Networking

DNS configuration details

General DNS setup

The OpenShift Container Platform cluster managed by CRC uses 2 DNS domain names, crc.testing and apps-crc.testing. The crc.testing domain is for core OpenShift Container Platform services. The apps-crc.testing domain is for accessing OpenShift applications deployed on the cluster.

For example, the OpenShift Container Platform API server is exposed as api.crc.testing while the OpenShift Container Platform console is accessed as console-openshift-console.apps-crc.testing. These DNS domains are served by a dnsmasq DNS container running inside the CRC instance.

The crc setup command detects and adjusts your system DNS configuration so that it can resolve these domains. Additional checks are done to verify DNS is properly configured when running crc start.

DNS on Linux

On Linux, depending on your distribution, CRC expects the following DNS configuration:

NetworkManager + systemd-resolved

This configuration is used by default on Fedora 33 or newer, and on Ubuntu Desktop editions.

CRC expects NetworkManager to manage networking.
CRC configures systemd-resolved to forward requests for the testing domain to the 192.168.130.11 DNS server. 192.168.130.11 is the IP of the CRC instance.
systemd-resolved configuration is done with a NetworkManager dispatcher script in /etc/NetworkManager/dispatcher.d/99-crc.sh:
```
#!/bin/sh

export LC_ALL=C

systemd-resolve --interface crc --set-dns 192.168.130.11 --set-domain ~testing

exit 0
```

systemd-resolved is also available as an unsupported Technology Preview on Red Hat Enterprise Linux and CentOS 8.3. After configuring the host to use systemd-resolved, stop any running clusters and rerun crc setup.

NetworkManager + dnsmasq

This configuration is used by default on Fedora 32 or older, on Red Hat Enterprise Linux, and on CentOS.

CRC expects NetworkManager to manage networking.
NetworkManager uses dnsmasq with the /etc/NetworkManager/conf.d/crc-nm-dnsmasq.conf configuration file.
The configuration file for this dnsmasq instance is /etc/NetworkManager/dnsmasq.d/crc.conf:
```
server=/crc.testing/192.168.130.11
server=/apps-crc.testing/192.168.130.11
```
- The NetworkManager dnsmasq instance forwards requests for the crc.testing and apps-crc.testing domains to the 192.168.130.11 DNS server.

Reserved IP subnets

The OpenShift Container Platform cluster managed by CRC reserves IP subnets for internal use, which should not collide with your host network. Ensure that the following IP subnets are available for use:

Reserved IP subnets

10.217.0.0/22
10.217.4.0/23
192.168.126.0/24

Additionally, the host hypervisor might reserve another IP subnet depending on the host operating system. No additional subnet is reserved on macOS and Microsoft Windows. The additional reserved subnet for Linux is 192.168.130.0/24.

Starting CRC behind a proxy

You can start CRC behind a defined proxy using environment variables or configurable properties.

SOCKS proxies are not supported by OpenShift Container Platform.

Prerequisites

If you are not using crc oc-env, when interacting with the cluster, export the .testing domain as part of the no_proxy environment variable. The embedded oc executable does not require manual settings. For more information about using the embedded oc executable, see Accessing the OpenShift cluster with the OpenShift CLI.

Procedure

Define a proxy using the http_proxy and https_proxy environment variables or using the crc config set command as follows:

$ crc config set http-proxy http://proxy.example.com:<port>
$ crc config set https-proxy http://proxy.example.com:<port>
$ crc config set no-proxy <comma-separated-no-proxy-entries>

If the proxy uses a custom CA certificate file, set it as follows:
```
$ crc config set proxy-ca-file <path-to-custom-ca-file>
```

Proxy-related values set in the configuration for CRC have priority over values set with environment variables.

Setting up CRC on a remote server

Configure a remote server to run an OpenShift Container Platform cluster provided by CRC.

This procedure assumes the use of a Red Hat Enterprise Linux, Fedora, or CentOS server. Run every command in this procedure on the remote server.

Perform this procedure only on a local network. Exposing an insecure server on the internet has many security implications.

Prerequisites

CRC is installed and set up on the remote server. For more information, see Installing CRC and Setting up CRC.
CRC is configured to use the OpenShift preset on the remote server. For more information, see Changing the selected preset.
Your user account has sudo permissions on the remote server.

Procedure

Start the cluster:
```
$ crc start
```
Ensure that the cluster remains running during this procedure.
Install the haproxy package and other utilities:
```
$ sudo dnf install haproxy /usr/sbin/semanage
```

Modify the firewall to allow communication with the cluster:

$ sudo systemctl enable --now firewalld
$ sudo firewall-cmd --add-service=http --permanent
$ sudo firewall-cmd --add-service=https --permanent
$ sudo firewall-cmd --add-service=kube-apiserver --permanent
$ sudo firewall-cmd --reload

For SELinux, allow HAProxy to listen on TCP port 6443 to serve kube-apiserver on this port:
```
$ sudo semanage port -a -t http_port_t -p tcp 6443
```
Create a backup of the default haproxy configuration:
```
$ sudo cp /etc/haproxy/haproxy.cfg{,.bak}
```

Configure haproxy for use with the cluster:

$ export CRC_IP=$(crc ip)
$ sudo tee /etc/haproxy/haproxy.cfg &>/dev/null <<EOF
global
    log /dev/log local0

defaults
    balance roundrobin
    log global
    maxconn 100
    mode tcp
    timeout connect 5s
    timeout client 500s
    timeout server 500s

listen apps
    bind 0.0.0.0:80
    server crcvm $CRC_IP:80 check

listen apps_ssl
    bind 0.0.0.0:443
    server crcvm $CRC_IP:443 check

listen api
    bind 0.0.0.0:6443
    server crcvm $CRC_IP:6443 check
EOF

Start the haproxy service:
```
$ sudo systemctl start haproxy
```

Connecting to a remote CRC instance

Use dnsmasq to connect a client machine to a remote server running an OpenShift Container Platform cluster managed by CRC.

This procedure assumes the use of a Red Hat Enterprise Linux, Fedora, or CentOS client. Run every command in this procedure on the client.

Connect to a server that is only exposed on your local network.

Prerequisites

A remote server is set up for the client to connect to. For more information, see Setting up CRC on a remote server.
You know the external IP address of the server.
You have the latest OpenShift CLI (oc) in your $PATH on the client.

Procedure

Install the dnsmasq package:
```
$ sudo dnf install dnsmasq
```

Enable the use of dnsmasq for DNS resolution in NetworkManager:

$ sudo tee /etc/NetworkManager/conf.d/use-dnsmasq.conf &>/dev/null <<EOF
[main]
dns=dnsmasq
EOF

Add DNS entries for CRC to the dnsmasq configuration:

$ sudo tee /etc/NetworkManager/dnsmasq.d/external-crc.conf &>/dev/null <<EOF
address=/apps-crc.testing/SERVER_IP_ADDRESS
address=/api.crc.testing/SERVER_IP_ADDRESS
EOF

Comment out any existing entries in /etc/NetworkManager/dnsmasq.d/crc.conf. These entries are created by running a local instance of CRC and will conflict with the entries for the remote cluster.

Reload the NetworkManager service:
```
$ sudo systemctl reload NetworkManager
```
Log in to the remote cluster as the developer user with oc:
```
$ oc login -u developer -p developer https://api.crc.testing:6443
```
The remote OpenShift Container Platform web console is available at https://console-openshift-console.apps-crc.testing.