Here’s another CAP idea I wanted to get out before I read a document I’ve been sent that may cover the same topic (just to make sure I don’t potentially draw on someone else’s idea). This concept came to me, again, last year whilst I was working on the CAENZ Public Alerting research report last year (I’m still waiting for this to be publicly released so I can link to it). My recent post proposing a browser plugin for CAP alerts is part of this bigger picture I am outlining today.

The background for it came from the realisation that there are a significant number of organisations in New Zealand that are responsible for the publication of alerts - whether to a secure group, or the general public. For example, there are 16 CDEMG Groups, 70 odd local authorities, GeoNet, MetService, Police and those responsible for infrastructure such as roads, and the Centre for Critical Infrastructure Protection.

Each of these agencies would need some means of hosting a CAP server, and incorporating some means of resilience into their CAP server(s). Given that there are potentially such a large number of CAP servers required, there are some aspects that could provide a strong and robust CAP network without seeing a proliferation of potentially fragile CAP servers. This is all built on the concept of a secure peer-to-peer network of CAP servers.

Federation
It should be possible to federate a group of CAP servers into a cluster. If we take a CDEM Group as an example, the group members may elect to deploy say 4 or 5 CAP servers to create a peer-to-peer network providing CAP alert hosting for the CDEM Group. Any authorised CAP message posted to one of the federated CAP servers would automatically distributed the CAP message to the other CAP servers in the federation. In this manner, the CAP message is instantly distributed and made available to other servers in the federation.

Peer-to-peer
I believe that the more robust approach to developing a CAP network is to base it upon peer-to-peer network technology, although tweaked to provide a secure means of publishing messages to the network These servers could of course be deployed any way to provide maximum resilience, and may be located close to major New Zealand Internet backbones, and quite possibly well outside of their geographic region. This has two potential benefits for resilience. Firstly, the message is available from multiple servers, so that the load (particularly for publicly accessible CAP servers) can be distributed across the multiple servers automatically. Secondly, should any particular server fail, the messages will still automatically be provided from the other CAP servers in the federation.

One example means by which this could be deployed is the following.

Provide a national CAP server network of federated CAP servers at key points - a nationally managed set of strategically located CAP servers. For example, Government internal CAP servers would be most likely located on the Government Shared Network (GSN) or whatever comes out of the recent restructure of this service. Public servers may be spread around both by geography and ISP (e.g. key ISPs may host a CAP server for their customers). In all circumstances these would fallback to other CAP servers in the federation in case of their failure.

Naturally, the open approach applied to peer-to-peer file sharing is not appropriate for a trusted network CAP service. To create a more secure network, something like a two-tier approach may be necessary.

CAP Publishing Servers
Private CAP publishing servers may be utilised to act as the publishing gateway to the public read-only peer-to-peer network provided by the CAP Read-only servers. Authentication, encryption and/or digital signing should be used as the basis to authorise the publication of a CAP message via the publishing server. The publishing server is responsible for verifying the digitally signed CAP alert, as well as the authentication details to verify the user is authorised to post the alert. Once authorised, the CAP publishing server publishes the alert to the road-only servers. This is the only channel to publishing CAP alerts to the network. Some form of CAP writing software (or service) may be useful for creating CAP messages and then publishing them to the servers. One protocol that may be useful for publishing is Atom as suggested by this IBM article.

CAP Read-only Servers
These are the user-facing servers that provide CAP messages to their end users. Only the CAP publishing servers are authorised to publish CAP messages to the peer-to-peer network for dissemination.

Naturally, this concept is part of a larger plan to build a CAP framework, and the circle would be able to be partly completed by designing web browser plugins that are capable of connecting to the peer-to-peer CAP read-only servers.

Widespread deployment of CAP browser plugins may mean that traditional servers may not be capable of supporting tens or hundreds of thousands of CAP clients regularly checking for new alerts. A peer-to-peer approach will probably provide the most scaleable and robust approach to disseminating CAP alerts via the Internet.

Originally posted on my blog, republished to TalkSahana.