Handle Foreach statement in Top Service Template of a Stacked Service

[Jerems]

Hi All and HNY 2022!

I am currently building a stacked-service which aims to create a Routing-Instance from which i can peer with different ISPs

This stacked-Service relies on 3 packages : 1 top service and 2 bottom service (components services)

The first bottom service handles Iface, link, vlan configurations.

The second bottom service handles the creation of the routing-instance a well as the BGP configuration part.

Because i believe that those two bottom components services can be reusable by some other top services i decided to create a top service that would import both bottom services.

This service creates 1 routing-instance, 1 security-zone and its associated security-policy as well as 1 BGP Group and  peer, 1 interface and 1 vlan.

How should i proceed to create 1 routing-instance  which could host multiple BGP Group depending on the CSP chosen from an enumeration list ?

Let's say that i can choose between ISP1, ISP2, ISP3. Each time i choose an ISP in my list, i am then able to navigate through the sub-items for that particular ISP (vlan, ip address, peer ip address, peer asn). At the moment, i use the same leaf which result in bad template outputs because the different values (for ISP1, ISP2...) of each leaf are concatenated :

<ip-address>192.168.255.9/30192.168.255.13/30</ip-address>

where it should be :

<ip-address(ISP1)>192.168.255.9/30</ip-address>

<ip-address(ISP2)>192.168.255.13/30</ip-address>

...and so on

Thanks in advance for your help !

[vleijon]

I am not quite sure what your problem is, but you may be able to use either a for-loop or an if-statement in your template. Check out the processing instructions part of the manual: https://developer.cisco.com/docs/nso/guides/#!templates/service-and-api-templates-in-multi-ned-environment

[Jerems]

Hi vleijon,

Thanks a lot for your answer. I am currently struggling with loops at the moment.

My routing instance is supposed to be able to host multiple BGP peerings with external ISPs.

Which means that for a particular Routing-instance i should be able to loop the creation of an interface with multiple vlan (list), each vlan could be assigned multiple IPs(list) :

This is what i expect :

routing-instance 1 > csp1 > vlan1 > IP1

                             > csp2 > vlan2 > IP2

This is what i obtain at the moment because of a strange loop :

routing-instance 1 > csp1 > vlan1 > IP1&2

                             > csp2 > vlan2 > IP1&2

CSP is a list, VLAN is a list and IP is a list

Thanks in advance for your help.

Jerems

[vleijon]

Hard to tell just from that, what is the yang type of IP1 and IP2? What is the corresponding fragment of the template? Perhaps you need an additional inner loop?

[Jerems]

Hi Vleijon,

I found my answer through the addition of loops in my top service. Thanks for your comment that corrobrates my findings !

To build my top service, i had to pick up the service part of my several bottom service templates but i wasn't sure on how to manage loops in my newly created top service. It becomes more & more clear to me

[vleijon]

Great to hear, one tip I want to share: You can do commit dry-run | debug template in the ncs_cli to get some extra debug information about your templates.

[Jerems]

Correct vleijon,

But honestly, i'm just a little bit confused when trying to understand the output of a "| debug template".

For /services/create_l3vpn:create_l3vpn[l3vpn_id='001']/devices[device='device1'], it evaluates to "device1"
Operation 'merge' on existing node: /devices/device[name='device1'] (from file "create_link-template.xml", line 5)
Processing instruction 'foreach': evaluating the node-set (from file "create_link-template.xml", line 9)
Evaluating "/junos/interface" (from file "create_link-template.xml", line 9)
Context node: /services/create_l3vpn:create_l3vpn[l3vpn_id='001']/devices[device='device1']
Result: empty node

For example, i often see this "empty node" result without having the ability to understand what is going wrong...

Thanks again !

[Jerems · Accepted solution]

In order to share my experience on creating a stacked service in NSO please find below a summary of the steps achieved to reach this goal.

To build some sort of usable stacked service design, one should consider the following hints or rules :

My project aimed to build a stacked service to allow the reuse of bottom packages (aka components) by different top services.

• Managing complexity in the top service, meaning that all conditions or loops (and all complex stuff) should be introduced in the upper service and not in the bottom one.
• Control the data types in your top service (you could even imagine of having only "string" types in the bottom services/packages)
• Consider each requested list in your yang design as a separate package. Imagine for example that you have to create a routing instance with all underlying components (Routing Policies, Routing Protocols, Associated interfaces). Instead of having one full package, you can have a package for each type of components. In my situation, i had for example a specific package to manage all BGP features. This will let me easily reuse the BGP package if i want to add a new peering in an existing service.

Does it mean that you should consider a Top Down approach ? Maybe yes. From my opinion, this is the best way to design your stack service, but it is still my own opinion

I will of course ask anyone of you comment, amend or even share his own personal experience on building stacked service.

Thanks again for the help provided by this great community ;-).