[Engine-devel] Fwd: Problem in REST API handling/displaying of logical networks

[Mike Kolesnik]

Hi All, 

I would like to hear opinions about a behaviour that I think is problematic in 
REST API handling of logical networks. 

-- Intro -- 
Today in the REST API we are exposing two collections for "logical 
network" related entities. 

First is a top level collection which is out of any context at the address 
http://engine/api/networks. 
Second is a sub-collection in the context of a cluster: 
http://engine/api/cluster/xxx/networks 

The network itself is defined per DC level, so for each DC you would have 
at least one logical network for management, which has some properties such 
as STP, MTU, etc.. 
The top level collection is used to create/delete such network entities. 

The sub-collection in the context of a Cluster is used to attach/detach a 
network from the DC of that cluster. 
The network in the context of a cluster has some additional information, let's 
say for example 'status' of the network: 
If a network is defined on all hosts in the cluster then it's status is 
'Operational'. 
If a network is not defined on some of the hosts in the cluster then it's 
status is 'Not Operational'[1]. 


-- Problem -- 
The problem is that details which are only relevant in context of a 
cluster, are still displayed in the root context as well (e.g: 'status'). 
This can, in certain cases, cause unexpected behaviour. 

For example, let's consider this topology: 
Data Center A 
| 
|\____ Network 'red' 
|\____ Cluster A1 
| \______ Network 'red' attached 
\____ Cluster A2 
\______ Network 'red' attached 

If the 'status' is the same on all the clusters that the network is attached to 
(A1, A2) then there will be one element in the top level collection, with the 
network details and the 'status' field representing the state (which is same 
for all networks in the cluster contexts of the cluster). 
If, however, the status is not the same (ie. on A1 the network is 
'Operational' and on A2 it is 'Non Operational') then the top-level 
collection will show two elements for the network, where all network 
details are the same and only the 'status' field is different. 

This is problematic IMHO for several reasons: 
1. Showing one network in certain states, and multiple copies of this 
network in other states is not optimal, to say the least. 
2. In the top-level collection there is no indicator of the cluster for which 
the network is displayed, so there is no way to differentiate between the 
two 'red' network elements (they will have same id, name, etc.). 
3. There is a certain asymmetry between the remove action[2] and the 
result in that you would expect: you either remove a network but in the 
result you would see several elements removed. 


-- Proposed Solutions -- 
Personally I can think of several solutions to this problem: 
1. Declare the top-level collection as a collection of all networks that are 
either attached to cluster or not, and if they are indeed attached then 
show the details for each cluster, including a link to the cluster. 
2. Declare the top-level collection as a collection of all networks that are 
defined in data-centers, but they will not contain any cluster specific 
data, and thus each entry is unique. 

Solution #2 is breaking the API backwards-compatibility, since it includes 
removing certain fields that have appeared today (namely 'status' and 
'display') but IMO would give a better experience since the top-level 
collection is actually used for managing networks, and not their attachment 
to clusters which should be done in the context of each cluster. 

I would like to hear what suggestions you have to solve this problem or if 
you prefer either of the above solutions. 


-- Footnotes -- 
[1] In 3.1 this is slightly different, but for the sake of simplicity I didn't 
specify the new behaviour. 
[2] Currently you can't update the network if it's attached to any cluster, 
but perhaps in the future this would be possible. 


Regards, 
Mike 


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