NVUE Snippets

NVUE supports both traditional snippets and flexible snippets:

  • Use traditional snippets to add configuration to the /etc/network/interfaces, /etc/frr/frr.conf, /etc/frr/daemons, /etc/cumulus/switchd.conf, /etc/cumulus/datapath/traffic.conf or /etc/ssh/sshd_config files.
  • Use flexible snippets to manage any other text file on the system.

  • A snippet configures a single parameter associated with a specific configuration file.
  • You can only set or unset a snippet; you cannot modify, partially update, or change a snippet.
  • Setting the snippet value replaces any existing snippet value.
  • Cumulus Linux supports only one snippet for a configuration file.
  • Only certain configuration files support a snippet.
  • NVUE does not parse or validate the snippet content and does not validate the resulting file after you apply the snippet.
  • PATCH is only the method of applying snippets and does not refer to any snippet capabilities.
  • As NVUE supports more features and introduces new syntax, snippets and flexible snippets become invalid. Before you upgrade Cumulus Linux to a new release, review the What's New for new NVUE syntax and remove the snippet if NVUE introduces new syntax for the feature that the snippet configures.

Traditional Snippets

Use traditional snippets if you configure Cumulus Linux with NVUE commands, then want to configure a feature that does not yet support the NVUE object model. You create a snippet in yaml format, then add the configuration to the file with the nv config patch command.

The nv config patch command requires you to use the fully qualified path name to the snippet .yaml file; for example you cannot use ./ with the nv config patch command.

/etc/frr/frr.conf Snippets

Example 1: Top Level Configuration

NVUE does not support configuring BGP to peer across the default route. The following example configures BGP to peer across the default route from the default VRF:

  1. Create a .yaml file with the following traditional snippet:

    cumulus@switch:~$ sudo nano bgp_snippet.yaml
    - set:
        system:
          config:
            snippet:
              frr.conf: |
                ip nht resolve-via-default
    
  2. Run the following command to patch the configuration:

    cumulus@switch:~$ nv config patch bgp_snippet.yaml
    
  3. Run the nv config apply command to apply the configuration:

    cumulus@switch:~$ nv config apply
    
  4. Verify that the configuration exists at the end of the /etc/frr/frr.conf file:

    cumulus@switch:~$ sudo cat /etc/frr/frr.conf
    ...
    ! end of router ospf block
    !---- CUE snippets ----
    ip nht resolve-via-default
    

Example 2: Nested Configuration

NVUE does not support configuring EVPN route targets using auto derived values from RFC 8365. The following example configures BGP to enable RFC 8365 derived router targets:

  1. Create a .yaml file with the following traditional snippet:

    cumulus@switch:~$ sudo nano bgp_snippet.yaml
    - set:
        system:
          config:
            snippet:
              frr.conf: |
                router bgp 65517 vrf default
                  address-family l2vpn evpn
                    autort rfc8365-compatible
    

Make sure to use spaces not tabs; the parser expects spaces in yaml format.

  1. Run the following command to patch the configuration:

    cumulus@switch:~$ nv config patch bgp_snippet.yaml
    
  2. Run the nv config apply command to apply the configuration:

    cumulus@switch:~$ nv config apply
    
  3. Verify that the configuration exists at the end of the /etc/frr/frr.conf file:

    cumulus@switch:~$ sudo cat /etc/frr/frr.conf
    ...
    ! end of router bgp 65517 vrf default
    !---- CUE snippets ----
    router bgp 65517 vrf default
    address-family l2vpn evpn
    autort rfc8365-compatible
    

The traditional snippets for FRR write content to the /etc/frr/frr.conf file. When you apply the configuration and snippet with the nv config apply command, the FRR service goes through and reads in the /etc/frr/frr.conf file.

/etc/network/interfaces Snippets

MLAG Timers Example

NVUE supports configuring only one of the MLAG service timeouts (initDelay). The following example configures the MLAG peer timeout to 400 seconds:

  1. Create a .yaml file and add the following traditional snippet:

    cumulus@switch:~$ sudo nano mlag_snippet.yaml
    - set:
        system:
          config:
            snippet:
              ifupdown2_eni:
                peerlink.4094: |
                  clagd-args --peerTimeout 400
    
  2. Run the following command to patch the configuration:

    cumulus@switch:~$ nv config patch mlag_snippet.yaml
    
  3. Run the nv config apply command to apply the configuration:

    cumulus@switch:~$ nv config apply
    
  4. Verify that the configuration exists in the peerlink.4094 stanza of the /etc/network/interfaces file:

    cumulus@switch:~$ sudo cat /etc/network/interfaces
    ...
    auto peerlink.4094
    iface peerlink.4094
     clagd-args --peerTimeout 400
     clagd-peer-ip linklocal
     clagd-backup-ip 10.10.10.2
     clagd-sys-mac 44:38:39:BE:EF:AA
     clagd-args --initDelay 180
    ...
    

Traditional Bridge Example

NVUE does not support configuring traditional bridges. The following example configures a traditional bridge called br0 with the IP address 11.0.0.10/24. swp1, swp2 are members of the bridge.

  1. Create a .yaml file and add the following traditional snippet:

    cumulus@switch:~$ sudo nano bridge_snippet.yaml
    - set:
        system:
         config:
           snippet:
             ifupdown2_eni:
               eni_stanzas: |
                 auto br0
                 iface br0
                   address 11.0.0.10/24
                   bridge-ports swp1 swp2
                   bridge-vlan-aware no
    
  2. Run the following command to patch the configuration:

    cumulus@switch:~$ nv config patch bridge_snippet.yaml
    
  3. Run the nv config apply command to apply the configuration:

    cumulus@switch:~$ nv config apply
    
  4. Verify that the configuration exists at the end of the /etc/network/interfaces file:

    cumulus@switch:~$ sudo cat /etc/network/interfaces
    ...
    auto br0
    iface br0
      address 11.0.0.10/24
      bridge-ports swp1 swp2
      bridge-vlan-aware no
    

/etc/cumulus/datapath/traffic.conf Snippets

To add data path configuration for the Cumulus Linux switchd module that NVUE does not yet support, create a traffic.conf snippet.

The following example creates a file called traffic_conf_snippet.yaml and enables the resilient hash setting.

  1. Create a .yaml file and add the following traditional snippet:

    cumulus@switch:~$ sudo nano traffic_conf_snippet.yaml
    - set:
        system:
          config:
            snippet:
              traffic.conf: |
                resilient_hash_enable = TRUE
    
  2. Run the following command to patch the configuration:

    cumulus@switch:~$ nv config patch traffic_conf_snippet.yaml
    
  3. Run the nv config apply command to apply the configuration:

    cumulus@switch:~$ nv config apply
    
  4. Verify that the configuration exists at the end of the /etc/cumulus/datapath/traffic.conf file:

    cumulus@switch:~$ sudo cat /etc/cumulus/datapath/traffic.conf
    ...
    !---- NVUE snippets ----
    resilient_hash_enable = TRUE
    

/etc/snmp/snmpd.conf Snippets

To add Cumulus Linux SNMP agent configuration not yet available with NVUE commands, create an snmpd.conf snippet.

The following example creates a file called snmpd.conf_snippet.yaml, and sets the read only community string and the listening address to run in the mgmt VRF.

  1. Create a .yaml file and add the following traditional snippet:

    cumulus@switch:~$ sudo nano snmpd.conf_snippet.yaml
    - set:
        system:
          config:
            snippet:
              snmpd.conf: |
                rocommunity cumuluspassword default
                agentaddress udp:@mgmt:161
    
  2. Run the following command to patch the configuration:

    cumulus@switch:~$ nv config patch snmpd.conf_snippet.yaml
    
  3. Run the nv config apply command to apply the configuration:

    cumulus@switch:~$ nv config apply
    
  4. Verify that the configuration exists at the end of the /etc/snmp/snmpd.conf file:

    cumulus@switch:~$ sudo cat /etc/snmp/snmpd.conf
    ...
    !---- NVUE SNMP Server Snippets ----
    rocommunity cumuluspassword default
    agentaddress udp:@mgmt:161
    

/etc/ssh/sshd_config Snippets

To add SSH service configuration not yet available with NVUE commands, create an sshd_config snippet.

The following example creates a file called sshd_config_snippet.yaml to allow root login and enable X11 forwarding for all users except user anoncvs. The snippet also disables TCP forwarding for the anoncvs user and runs the cvs server command when anoncvs logs in.

  1. Create a .yaml file and add the following traditional snippet:

    cumulus@switch:~$ sudo nano sshd_config_snippet.yaml
    - set:
        system:
          config:
            snippet:
              sshd_config: |
                PermitRootLogin yes
                X11Forwarding yes
                Match User anoncvs
                   X11Forwarding no
                   AllowTcpForwarding no
                   ForceCommand cvs server
    
  2. Run the following command to patch the configuration:

    cumulus@switch:~$ nv config patch sshd_config_snippet.yaml
    
  3. Run the nv config apply command to apply the configuration:

    cumulus@switch:~$ nv config apply
    
  4. Verify that the configuration exists at the end of the /etc/ssh/sshd_config file:

    cumulus@switch:~$ sudo cat /etc/ssh/sshd_config
    ...
    !---- NVUE snippets ----
    PermitRootLogin yes
    X11Forwarding yes
    Match User anoncvs
       X11Forwarding no
       AllowTcpForwarding no
       ForceCommand cvs server
    

Flexible Snippets

Flexible snippets are an extension of traditional snippets that let you manage any text file on the system.

  • You can create new files or modify existing files that NVUE does not manage.
  • You can add configuration to files that NVUE manages.

The account you use through the CLI or the REST API to configure and manage flexible snippets must be in the sudo group, which includes the NVUE system-admin role, or you must be the root user.

Files NVUE Manages

You can use flexible snippets to add configuration to the following files that NVUE manages:

Filename
Description
/etc/cumulus/csmgrdConfiguration file for csmgrctl commands.
/etc/default/isc-dhcp-relay-<VRF>Configuration file for DHCP relay. Changes to this file require a dhcrelay@<VRF>.service restart.
/etc/resolv.confConfiguration file for DNS resolution.
/etc/hostsConfiguration file for the hostname of the switch.
/etc/default/isc-dhcp-server-<VRF>Configuration file for DHCP servers. Changes to this file require a dhcpd@<VRF>.service restart.
/etc/default/isc-dhcp-server6-<VRF>Configuration file for DHCP servers for IPv6. Changes to this file require a dhcpd6@<VRF>.service restart
/etc/dhcp/dhcpd-<VRF>.confConfiguration file for the dhcpd service. Changes to this file require a dhcpd@<VRF>.service restart
/etc/dhcp/dhcpd6-<VRF>.confConfiguration file for the dhcpd service for IPv6. Changes to this file require a dhcpd6@<VRF>.service restart
/etc/ntp.confConfiguration file for NTP servers. Changes to this file require an ntp service restart.
/etc/default/isc-dhcp-relay6-<VRF>Configuration file for DHCP relay for IPv6. Changes to this file require a dhcrelay6@<VRF>.service restart.
/etc/snmp/snmpd.confConfiguration file for SNMP. Changes to this file require an snmpd restart.
/etc/cumulus/datapath/traffic.confConfiguration file for forwarding table profiles. Changes to this file require a switchd restart.
/etc/cumulus/switchd.confConfiguration file for switchd. Changes to this file require a switchd restart.

Flexible snippets do not support:

  • Binary files.
  • Symbolic links.
  • More than 1MB of content.
  • More than one flexible snippet in the same destination file.

Use caution when creating flexible snippets:

  • If you configure flexible snippets incorrectly, they might impact switch functionality. For example, even though flexible snippet validation allows you to only add textual content, Cumulus Linux does not prevent you from creating a flexible snippet that adds to sensitive text files, such as /boot/grub.cfg and /etc/fstab or add corrupt contents. Such snippets might render the switch unusable or create a potential security vulnerability (the NVUE service (nvued) runs with superuser privileges).
  • Do not manually update configuration files to which you add flexible snippets.
  • Any sensitive data in plain text (such as passwords) appears in the NVUE-managed configuration files as plain text.

Create a Flexible Snippet

To create a flexible snippet:

  1. Create a file in yaml format and add each flexible snippet you want to apply in the format shown below. NVUE appends the flexible snippet at the end of an existing file. If the file does not exist, NVUE creates the file, then adds the content.

    cumulus@leaf01:mgmt:~$ sudo nano <filename>.yaml>
    - set:
        system:
         config:
           snippet:
             <snippet-name>:
               file: "<filename>"
               permissions: "<umask-permissions>"
               content: |
                 # This is my content
               services:
                  <name>:
                    service: <service-name>
                    action: <action>
    
    • You can only set the umast permissions to a new file that you create. Adding the permissions: line is optional. The default umask persmissions are 644.
    • You can add a service with an action, such as start, restart, or stop. Adding the services: lines is optional; however, if you add the service: line, you must specify at least one service.
  2. Run the following command to patch the configuration:

    cumulus@switch:~$ nv config patch <filename>.yaml>
    
  3. Run the nv config apply command to apply the configuration:

    cumulus@switch:~$ nv config apply
    
  4. Verify the patched configuration.

The nv config patch command requires you to use the fully qualified path name to the snippet .yaml file; for example you cannot use ./ with the nv config patch command.

Flexible Snippet Examples

The following example flexible snippet called crontab-flex-snippet appends the single line @daily /opt/utils/run-backup.sh to the existing /etc/crontab file, then restarts the cron service.

cumulus@leaf01:mgmt:~$ sudo nano crontab-flex-snippet.yaml
- set:
    system:
      config:
        snippet:
          crontab-flex-snippet:
            file: "/etc/crontab"
            content: |
              @daily /opt/utils/run-backup.sh
            services:
              schedule:
                service: cron
                action: restart

The following example flexible snippet called apt-flex-snippet creates a new file /etc/apt/sources.list.d/microsoft-prod.list with 0644 permissions and adds multi-line text:

- set:
    system:
      config:
        snippet:
          apt-flexible-snippet:
            file: "/etc/apt/sources.list.d/microsoft-prod.list"
            content: |
              # Adding Microsoft SQL Server Sources
              deb [arch=amd64] https://packages.microsoft.com/debian/10/prod buster main
            permissions: "0644"

If you try to apply a flexible snippet to a file that NVUE does not allow, you see an error message similar to the following:

cumulus@leaf01:mgmt:~$ nv config apply
Invalid config [rev_id: 8]
  Flexible snippets are not allowed to be configured on the file '/etc/cumulus/ports.conf’.
  Flexible snippets are not allowed to be configured on the file '/etc/cumulus/ports_width.conf’.

If you try to apply a flexible snippet to a file that supports traditional snippets, you see an error message similar to the following:

cumulus@leaf01:mgmt:~$ nv config apply
Invalid config [rev_id: 1]
  Flexible snippet cannot be used to modify the file '/etc/ssh/sshd_config'. Traditional snippets (for e.g., 'sshd_config') are supported on this file. Consult NVIDIA NVUE documentation for further information on snippets.

You can also create a flexible snippet with the REST API. See NVUE API.

Remove a Snippet

To remove a traditional or flexible snippet, edit the snippet’s .yaml file to change set to unset, then patch and apply the configuration. Alternatively, you can use the REST API DELETE and PATCH methods.

The following example removes the MLAG timer traditional snippet created above to configure the MLAG peer timeout:

  1. Edit the mlag_snippet.yaml file to change set to unset:

    cumulus@switch:~$ sudo nano mlag_snippet.yaml
    - unset:
        system:
          config:
            snippet:
              ifupdown2_eni:
    
  2. Run the following command to patch the configuration:

    cumulus@switch:~$ nv config patch mlag_snippet.yaml
    
  3. Run the nv config apply command to apply the configuration:

    cumulus@switch:~$ nv config apply
    
  4. Verify that the peer timeout parameter no longer exists in the peerlink.4094 stanza of the /etc/network/interfaces file:

    cumulus@switch:~$ sudo cat /etc/network/interfaces
    ...
    auto peerlink.4094
    iface peerlink.4094
     clagd-peer-ip linklocal
     clagd-backup-ip 10.10.10.2
     clagd-sys-mac 44:38:39:BE:EF:AA
     clagd-args --initDelay 180
    ...