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.

Cumulus Linux stores all snippets in the /system/config/snippet directory.

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:

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

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

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:

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.

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

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.

Example 3: EVPN Multihoming FRR Debugging

NVUE does not support configuring FRR debugging for EVPN multihoming. The following example configures FRR debugging:

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

cumulus@switch:~$ sudo nano mh_debug_snippet.yaml
- set:
    system:
      config:
        snippet:
          frr.conf: |
            debug bgp evpn mh es
            debug bgp evpn mh route
            debug bgp zebra
            debug zebra evpn mh es
            debug zebra evpn mh mac
            debug zebra evpn mh neigh
            debug zebra evpn mh nh
            debug zebra vxlan

Run the following command to patch the configuration:

cumulus@switch:~$ nv config patch mh_debug_snippet.yaml

Run the nv config apply command to apply the configuration:
```
cumulus@switch:~$ nv config apply
```

Verify that the configuration exists in the /etc/frr/frr.conf file:

cumulus@switch:~$ sudo cat /etc/frr/frr.conf
...
!---- NVUE snippets ----
debug bgp evpn mh es
debug bgp evpn mh route
debug bgp zebra
debug zebra evpn mh es
debug zebra evpn mh mac
debug zebra evpn mh neigh
debug zebra evpn mh nh
debug zebra vxlan

/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:

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

Run the following command to patch the configuration:

cumulus@switch:~$ nv config patch mlag_snippet.yaml

Run the nv config apply command to apply the configuration:
```
cumulus@switch:~$ nv config apply
```

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.

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

Run the following command to patch the configuration:

cumulus@switch:~$ nv config patch bridge_snippet.yaml

Run the nv config apply command to apply the configuration:
```
cumulus@switch:~$ nv config apply
```

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/switchd.conf Snippets

NVUE does not provide options to configure link flap detection settings. The following example configures the link flap window to 10 seconds and the link flap threshold to 5 seconds:

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

cumulus@switch:~$ sudo nano switchd_snippet.yaml
- set:
    system:
      config:
        snippet:
          switchd.conf: |
            link_flap_window = 10
            link_flap_threshold = 5

Run the following command to patch the configuration:

cumulus@switch:~$ nv config patch switchd_snippet.yaml

Run the nv config apply command to apply the configuration:
```
cumulus@switch:~$ nv config apply
```

Verify that the configuration exists at the end of the /etc/cumulus/switchd.conf file:

cumulus@switch:~$ sudo cat /etc/cumulus/switchd.conf
!---- NVUE snippets ----
link_flap_window = 10
link_flap_threshold = 5

/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.

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

Run the following command to patch the configuration:

cumulus@switch:~$ nv config patch traffic_conf_snippet.yaml

Run the nv config apply command to apply the configuration:
```
cumulus@switch:~$ nv config apply
```

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

Flexible Snippets

Flexible snippets are an extension of traditional snippets that let you manage any text file on the system. You can add content to an existing text file or create a new text file, then add content. Cumulus Linux runs flexible snippets as root.

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 box unusable or create a potential security vulnerability (the NVUE service (nvued) runs with superuser privileges).
Do not add flexible snippets to configuration files that NVUE already controls, such as the /etc/hosts, /etc/ntp.conf, or /etc/ptp4l.conf files. Cumulus Linux does not prevent you from creating and applying a flexible snippet to these files and does not show warnings or errors. Cumulus Linux might accept the snippet content without adding it in the file. For a list of the files that NVUE manages, refer to Configuration Files that NVUE Manages.
Do not manually update configuration files to which you add flexible snippets.

To create flexible snippets:

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

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:

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

cumulus@switch:~$ sudo nano mlag_snippet.yaml
- unset:
    system:
      config:
        snippet:
          ifupdown2_eni:

Run the following command to patch the configuration:

cumulus@switch:~$ nv config patch mlag_snippet.yaml

Run the nv config apply command to apply the configuration:
```
cumulus@switch:~$ nv config apply
```

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
...

NVUE Snippets

Traditional Snippets

/etc/frr/frr.conf Snippets

Example 1: Top Level Configuration

Example 2: Nested Configuration

Example 3: EVPN Multihoming FRR Debugging

/etc/network/interfaces Snippets

MLAG Timers Example

Traditional Bridge Example

/etc/cumulus/switchd.conf Snippets

/etc/cumulus/datapath/traffic.conf Snippets

Flexible Snippets

Flexible Snippet Examples

Remove a Snippet

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