foreach in template

[ian.scheidler1]

Hi,

I have a problem which I really dont understand. In one case it works, in another it doesnt.

Let's start with what works:

YANG:

leaf-list iphelper {
       type inet:ipv4-address {
       }
    }

The Leaf List is filled with data from WebUI:

Template:

<ip>
    <address>
        <primary>
            <address>{/gw_ip}</address>
            <mask>{/subnetmask_usernet}</mask>
        </primary>
    </address>
    <?foreach {/iphelper}?>
        <helper-address><!--for each, input list-->
            <helper-address-list>
	        <address>{/iphelper}</address>
	    </helper-address-list>
            </helper-address>
     <?end?>

This correctly generates multiple iphelper entries in the config for every item in the list. Like this:

interface Vlan975
 ip vrf forwarding db-sus-ri
 ip address 192.168.2.1 255.255.255.0
 ip helper-address 192.168.33.3
 ip helper-address 192.168.44.4
 ip helper-address 192.168.55.5
 no shutdown
 no autostate
exit

So far so good. This all works. :)

I am now trying to apply the same pattern to a List of IP prefixes:

YANG:

leaf-list prefixlist {
      type inet:ipv4-address { //TODO: type here should be inet:ipv4-prefix (e.g. xxx.xxx.xxx.xxx/xx)
      }
    }

Here is actually my first problem. If I use the inet:ipv4-prefix data type it is somehow impossible to fill the list from the WebUI (when i click on + an input field opens up and I can enter a prefix but when I click OK the input field closes but it just doesnt show up in the list in the WebUI). Haven't actually tried yet from CLI as customer wants the WebUI and I also believe it should be possible from both. Any ideas on this?

Template:

<ip>
<!-- ...here is some vrf config which I left out here... -->
<prefix-list><!--foreach seq 50-->
    <prefixes>
        <name>PL_{$vrf_name}_bgp2ebgp</name>
            <seq>
               <no>5</no>
               <permit>
                   <ip>0.0.0.0/0</ip>
               </permit>
            </seq>
    </prefixes>
    <prefixes>
        <name>PL_{$vrf_name}_ebgp2bgp</name>
        <seq>
           <no>5</no>
           <permit>
              <ip>10.242.0.0/16</ip>
              <le>30</le>
           </permit>
        </seq>
        <seq>
            <no>10</no>
            <permit>
                <ip>10.243.0.0/16</ip>
                <le>30</le>
            </permit>
        </seq>
        <seq>
            <no>15</no>
            <permit>
                <ip>10.244.0.0/16</ip>
                <le>30</le>
            </permit>
        </seq>
        <seq>
            <no>20</no>
            <permit>
                <ip>10.245.0.0/16</ip>
                <le>30</le>
            </permit>
        </seq>
        <seq>
            <no>25</no>
            <permit>
                <ip>10.246.0.0/16</ip>
                <le>30</le>
            </permit>
        </seq>
        <seq>
            <no>30</no>
            <permit>
                <ip>10.247.0.0/16</ip>
                <le>30</le>
            </permit>
        </seq>
        <seq>
            <no>35</no>
            <permit>
                <ip>10.248.0.0/16</ip>
                <le>30</le>
            </permit>
        </seq>
        <seq>
            <no>40</no>
            <permit>
                <ip>10.249.0.0/16</ip>
                <le>30</le>
            </permit>
        </seq>
        <seq>
            <no>45</no>
            <permit>
                <ip>10.250.0.0/16</ip>
                <le>30</le>
            </permit>
        </seq>
        <?foreach {/prefixlist}?>
        <seq>
            <no>50</no>
            <permit>
                <ip>{/prefixlist}</ip>
                <le>30</le>
            </permit>
        </seq>
        <?end?>
    </prefixes>
</prefix-list>
</ip>

As you can hopefully see the prefix data up to line (<no>) 45 is static and everything after that should be added from the leaf list entries.

I get the following error:

Python cb_create error. Unknown error (66): DBS_VPN-template.xml:103 Expression '{/prefixlist}' resulted in an incompatible value '192.168.44.4192.168.55.5192.168.66.6' for /ncs:devices/device{IOSdev0}/config/ios:ip/prefix-list/prefixes{PL_db-sus-ri_ebgp2bgp}/seq{50}/permit/ip

I understand that NSO tries to apply the entire list (concatenated together) as one value, which doesn't work.

But why does this work for IP helper? And how else do I access the single items of the list otherwise?

[yfherzog]

Hi,

On the helper address list, you're pushing configs into multiple list entries, as 'address' is a key in a list called helper-address-list.

On the second example, 'permit' is a container, so it can only take one value, and you provide it with the complete content of your list of prefixes.

You might want to create multiple entries of the 'seq' list, providing a running sequence to 'no' (currently you use 50 for all iterations).

Also, be careful when you use the '/' inside your templates (e.g. /prefixlist).

It actually resets the execution context in the template engine.

Use 'commit dry-run | debug template' to debug the process.

Finally, I tend to think that your first example will work even if you remove the foreach statement (give it a try).

[ian.scheidler1]

Hi thanks.

OK I will try the first example without foreach and see if it works (from your explanatin I also believe it will work).

As for the second example

OK...I also need some sort of counter which increments in steps of 5. How can I have such a counter in the template (or rather in the foreach)?

And how do I tell NSO to only use the current entry of the leaf list in each iteration?

If you could provide me with a (small) code example I would be very grateful!

[yfherzog · Accepted solution]

Doing the second bit in templates-only might not be that trivial, but can be done in python.

This can be part of your template:

<config-template xmlns="http://tail-f.com/ns/config/1.0">

  <devices xmlns="http://tail-f.com/ns/ncs">

    <device>

      <name>{/device}</name>

      <config>

        <interface xmlns="urn:ios">

          <Vlan>

            <name>975</name>

            <ip>

              <helper-address>

                <helper-address-list>

                  <address>{/iphelper}</address>

                </helper-address-list>

              </helper-address>

            </ip>

          </Vlan>

        </interface>

        <ip xmlns="urn:ios">

          <prefix-list>

            <prefixes>

              <name>PL_foo</name>

              <seq>

                <no>5</no>

                <permit>

                  <ip>1.1.1.1/32</ip>

                </permit>

              </seq>

              <seq>

                <no>{$SEQ}</no>

                <permit>

                  <ip>{$PREFIX}</ip>

                </permit>

              </seq>

            </prefixes>

          </prefix-list>

        </ip>

      </config>

    </device>

  </devices>

</config-template>

and this can be the python code to apply the template:

   @service.create

    def cb_create(self, tctx, root, service, proplist):

        self.log.info('Service create(service=', service._path, ')')

        vars = ncs.template.Variables()

        seq = 50

        for prefix in service.prefixlist:

            vars.add('SEQ', seq)

            vars.add('PREFIX', prefix + '/32')

            template = ncs.template.Template(service)

            template.apply('ian-template', vars)

            seq = seq + 10

It might have been cleaner to split the template into static part and dynamic part and only apply the dynamic part multiple times, but the result is the same.

[pmarcais]

How would you do the python for loop to a yang 'list' with few leaf instead of 'leaf-list' as mentioned in your example?

For example :

list prefixlist {
      key prefix;
      leaf prefix {
        type string;
      }
      leaf id {
        type string;
      }
      leaf length {
        type string;
      }
    }

Something like that:

 for prefix in service.prefixlist:

           self.log.info('DEBUG:(interface=', prefix, ')')

           self.log.info('DEBUG:(id=', service.prefixlist.id, ')')

           self.log.info('DEBUG:(length=', service.prefixlist.length, ')')

I can't make it work.

Thanks

[yfherzog]

Not sure exactly what's not working, but your prints should look something like this:

 for prefix in service.prefixlist:
           self.log.info('DEBUG:(interface=', prefix.prefix, ')')
           self.log.info('DEBUG:(id=', prefix.id, ')')
           self.log.info('DEBUG:(length=', prefix.length, ')')

[pmarcais]

Thanks a lot it works now! I see my mistake now.

[Michael Maddern · Accepted solution]

Hi Ian,

I think, as you already discussed, you don't always need the foreach. The template will loop automatically. But if you want to explicitly loop, you can refer to current interation using current() or .

You could set a variable to store the counter. So something like:

<?set counter={0}?>
<?foreach {/prefixlist}?>
<seq>
  <no>{$counter}</no>
  <permit>
    <ip>{current()}</ip>
    <le>30</le>
  </permit>
  <?set counter={$counter + 5}?>
</seq>
<?end?>