How to properly use the value of an existing node in `foreach` in a device template

[juacosta]

I want to remove all dns-servers in an ios device. I created the following template attempting to remove the existing DNS servers

<config xmlns="http://tail-f.com/ns/config/1.0">
  <devices xmlns="http://tail-f.com/ns/ncs">
  <device>
    <name>{$DEVICE_NAME}</name>
      <config>
      <ip xmlns="urn:ios">
      <dhcp>
        <pool>
          <id>LAN-POOL</id>
          <?foreach {dns-server}?>
             <dns-server tags="delete">{dns-server}</dns-server>
          <?end?>
        </pool>
      </dhcp>
      </ip>
      </config>
  </device>
  </devices>
</config>

NSO process the template successfully but the config remains. It seems the way I am dereferencing the value of the dns-server node it is not correct.

I attempted a variation, I made {dns-server} to be {/dns-server} and "/dns-server" was interpreted as a value and it looks like a new entry will be added when I do a sh template

[edit]
admin@ncs% show devices template BBB
config {
    ios:ip {
        dhcp {
            pool LAN-POOL {
                dns-server [ "{/dns-server}" ];
            }
        }
    }
}
[ok][2019-05-10 13:31:17]

[edit]
admin@ncs%

This is the original config I want to remove <dns-server> entries from

admin@ncs% show devices device CPE-c2d09c6c-6688-4b3f-b74a-f9fb18be6326 config ios:ip dhcp pool | display xml
<config xmlns="http://tail-f.com/ns/config/1.0">
  <devices xmlns="http://tail-f.com/ns/ncs" tags=" merge ">
  <device>
    <name>CPE-c2d09c6c-6688-4b3f-b74a-f9fb18be6326</name>
      <config>
      <ip xmlns="urn:ios">
      <dhcp>
      <pool refcounter="2"  backpointer="[ /vmsservice:ufp/vmsservice:vmsservice[vmsservice:name='CPE-c2d09c6c-6688-4b3f-b74a-f9fb18be6326'] ]" >
        <id>LAN-POOL</id>
        <network>
          <network-number>172.26.0.0</network-number>
        </network>
        <dns-server>172.16.1.102</dns-server>
        <dns-server>172.16.2.103</dns-server>
        <dns-server>172.16.2.104</dns-server>
        <domain-name>msx.cisco.com</domain-name>
      </pool>
      </dhcp>
      </ip>
      </config>
  </device>
  </devices>
</config>
[ok][2019-05-10 14:04:15]

[edit]
admin@ncs%

Any thoughts ?

[vleijon]

This looks like an attempt to delete a list of dns-servers that you define in your service model. But it sounds like you actually want to delete all pre-existing dns-servers and that is actually much easier.

A tempalte to delete all dns-servers looks something like this:

       <ip xmlns="urn:ios">
         <dhcp>
           <pool>
             <id>LAN-POOL</id>
             <dns-server tags="delete"></dns-server>
           </pool>
         </dhcp>
       </ip>

[juacosta]

@vleijon Thanks a lot for the response. I tried and that fails with this error

y error: <rpc-reply xmlns="urn:ietf:params:xml:ns:netconf:base:1.0" xmlns:nc="urn:ietf:params:xml:ns:netconf:base:1.0" message-id="1">
  <rpc-error>
    <error-type>application</error-type>
    <error-tag>operation-failed</error-tag>
    <error-severity>error</error-severity>
    <error-message unknown:lang="en">Exception in callback: Exception while applying template to device CPE-c2d09c6c-6688-4b3f-b74a-f9fb18be6326 message /ncs:devices/template{RemovingDNSConfigs}/config/ip/dhcp/pool{LAN-POOL}/dns-server{""}: Expression '' resulted in an incompatible value '' for /ncs:devices/device{CPE-c2d09c6c-6688-4b3f-b74a-f9fb18be6326}/config/ip/dhcp/pool{LAN-POOL}/dns-server</error-message>
  </rpc-error>
</rpc-reply>

    at com.cisco.vms.orchestrationservice.nso.NSOClient.handleEditConfig(NSOClient.java:219)
    at com.cisco.vms.orchestrationservice.stream.handler.OrchestrationMessageProcessor.submitRequest(Orchestration

Running on NSO 4.7.1.

I think it fails because the XPATH query will not be able to find a match. I tried the abbreviated form before trying to use foreach with  

<dns-server tags="delete" />

[vleijon]

There is something weird going on there, try doing | debug template and sharing the template itself and we might be able to figure it out.

[juacosta]

This is the template I am using

<config xmlns="http://tail-f.com/ns/config/1.0">
  <devices xmlns="http://tail-f.com/ns/ncs">
  <device>
    <name>{$DEVICE_NAME}</name>
      <config>
      <ip xmlns="urn:ios">
      <dhcp>
        <pool>
          <id>LAN-POOL</id>
          <dns-server tags="delete"></dns-server>
        </pool>
      </dhcp>
      </ip>
      </config>
  </device>
  </devices>
</config>

[vleijon]

Sorry, I have no idea why the template doesn't work for you even tough it does for you. You can try doing your commit | debug template  or | debug service to try and find more information,

[juacosta]

The best debug information I was able to retrieve is this

[edit]
admin@ncs% request devices device CPE-4a07e720-f89f-447b-8a0d-5cf4b3c46542 apply-template template-name Clean\ Previous\ DNS\ Servers | debug template
Operation 'merge' on existing node: /devices/device[name='CPE-4a07e720-f89f-447b-8a0d-5cf4b3c46542']
Fetching literal "LAN-POOL"
Operation 'merge' on existing node: /devices/device[name='CPE-4a07e720-f89f-447b-8a0d-5cf4b3c46542']/config/ios:ip/dhcp/pool[id='LAN-POOL']
Fetching literal []
Error: 'devices template "Clean Previous DNS Servers" config ip dhcp pool LAN-POOL dns-server ""': Expression '' resulted in an incompatible value '' for 'devices device CPE-4a07e720-f89f-447b-8a0d-5cf4b3c46542 config ip dhcp pool LAN-POOL dns-server'
[error][2019-05-10 22:20:14]

[edit]
admin@ncs% 

I think the Fetching Literal [] confirms XPATH is looking for non empty value in the <dns-server tags=delete></dns-server>