Is it possible to subscribe to mail events on an IBM Domino server?
I need a service similar to the one provided by Microsoft Exchange Event Notification, where you can subscribe to events and get notified when there are changes - eg. arrival of a new e-mail. I need the solution to be server side, since I can't rely on users having their client running.
Unfortunately, as per my comment above, there is no pre-packaged equivalent to the push, pull and streaming subscription services that EWS supports. A Notes client can get notifications via Notes RPC protocol, and there's also obviously some technology in IBM's Notes Traveler mobile product, but nothing that I'm aware of as a pre-packed web service or even as a notifications API. You would have to build it. There are a variety of ways you could go about it.
For push or streaming subscriptions, one way would be with a Notes C API plugin using the Extension Manager, running on the server and monitoring the mailboxes. You might be able to use a DSAPI plugin into Domino's HTTP stack to manage the incoming connections and feed the data out to subscribers, but honestly I have no idea if Domino's HTTP stack can handle the persistent connections that are implied in the subscription model. Alternatively, the Extension Manager plugin could quickly send the data over to code written in any other language that you want, running on any web stack that. Of course, you'll have to deal with security through all the linked-together parts.
For pull subscriptions, I guess it's really more of a polling archiecture, with state saved somewhere so that only changes since the last call will be delivered. You have any number of options for that. You could use Domino's built-in HTTP server, obviously, so you could write your own Domino-hosted web service for this. You could also use the Domino Data Service, which is a REST API, to do this -- with all necessary state information being stored on the client-side. (On quick look, I don't see a good option for getting all new docs since a specified date-time via Domino Data Service, but it might be possible.)
I do worry a bit about scalability of any custom solution for this. My understanding is that Microsoft has quite a bit of caching and optimization in their services in order to address scale. Obviously, you can build whatever you need for that into your own web service, but it will likely add a lot of effort.
Related
I have a working monolith application (deployed in a container), for which I want to add notifications feature as a separate microservice.
I'm planning for the monolith to emit events to a message bus (RabbitMQ) where they will be received by the new service, which will send the notification to user. In order to compose a notification, it will need other information about the user from the monolit, so it will call monolith's REST API in order to obtain it.
The problem is, that access to the monolith's API requires authentication in form of a token. I was thinking of:
using the secret from the monolith to issue a never-expiring token - I don't think this is a great idea from the security perspective, and also I know that sometimes the keys rotate in which case the token would became invalid eventually anyway
using the message bus to retrieve the information - this does not seem a good idea either as the asynchrony would make it very complicated
providing all the info the notification service needs in the event - this would make them more coupled together, and moreover, I plan to also send notifications based on the state on the monolith not triggered by an event
removing the authentication from the monolith and implementing it differently (not sure how yet)
My question is, what are some of the good ways this kind of problem can be solved, and also, having just started learning about microservices, is what I am trying to do right in the first place?
When dealing with internal security you should always consider the deployment and how the APIs are exposed to the outside world, an API gateway might be used to simply make it impossible to access internal APIs. In that case, a fixed token might be good enough to ensure that the client is authorized.
In general, though, I would suggest looking into OAuth2 or a JWT-based solution as it helps to validate the identities of the calling system as well as their access grants.
As for your architecture doubts, you need to consider the following scenarios when building out the solution:
The remote call can fail, at any time for unknown reasons, as such you shouldn't acknowledge the notification event until you're certain that the notification has been processed successfully.
As you've mentioned RabbitMQ, you should aim to keep the notification queue as small as possible, to that effect, a cache that contains the user details might help speed things along (and help you reduce the chance of failure due to the external system not being available).
If your application sends a lot of notifications to potentially millions of different users, you could consider having a read-only database replica of the users which is accessible to the notification service, and directly read from the database cluster in batches. This reduces the load on the monolith and shift it to the database layer
We have multiple web and windows applications which were deployed to different servers that we are planning to integrate using NservierBus to let all apps can pub/sub message between them, I think we using pub/sub pattern and using MSMQ transport will be good for it. but one thing I am not clear if it is a way to avoid hard code to set sub endpoint to MSMQ QueueName#ServerName which has server name in it directly if pub is on another server. on 6-pre I saw idea to set endpoint name then using routing to delegate to transport-level address, is that a solution to do that? or only gateway is the solution? is a broker a good idea? what is the best practice for this scenario?
When using pub/sub, the subscriber currently needs to know the location of the queue of the publisher. The subscriber then sends a subscription-message to that queue, every single time it starts up. It cannot know if it subscribed already and if it subscribed for all the messages, since you might have added/configured some new ones.
The publisher reads these subscriptions messages and stores the subscription in storage. NServiceBus does this for you, so there's no need to write code for this. The only thing you need is configuration in the subscriber as to where the (queue of the) publisher is.
I wrote a tutorial myself which you can find here : http://dennis.bloggingabout.net/2015/10/28/nservicebus-publish-subscribe-tutorial/
That being said, you should take special care related to issues regarding websites that publish messages. More information on that can be found here : http://docs.particular.net/nservicebus/hosting/publishing-from-web-applications
In a scale out situation with MSMQ, you can also use the distributor : http://docs.particular.net/nservicebus/scalability-and-ha/distributor/
As a final note: It depends on the situation, but I would not worry too much about knowing locations of endpoints (or their queues). I would most likely not use pub/sub just for this 'technical issue'. But again, it completely depends on the situation. I can understand that rich-clients which spawn randomly might want this. But there are other solutions as well, with a more centralized storage and an API that is accessed by all the rich clients.
I'd like to create a web service that an application server can contact to add itself to a list of servers implementing the application. Clients could then contact the service to get a list of servers. Something similar to how minecraft's heartbeats work for adding your server to the main server list.
I could implement it myself pretty easily, but I'm hoping someone has already created something like this.
Advanced features would be useful. Things like:
Allowing a client to perform queries on application-specific properties like the number of users currently connected to the server
Distributing the server list across more than one machine
Timing out a server's entry in the list if it hasn't sent a heartbeat within some amount of time
Does anyone know of a service like this? I know there are open protocols and servers for doing local-LAN service discovery, but this would be a WAN service.
The protocols I could find that had any relevance to your intended application are these:
XRDS (eXtensible Resource Descriptor Sequence).
XMPP Service Discovery protocol.
The XRDS documentation is obtuse, but you may be able to push service descriptions in XML format. The service type specification might be generic, but I get a headache from trying to decipher committee-speak.
The XMPP Service Discovery protocol (part of the protocol Formerly Known As Jabber) also looked promising, but it seems that even though you could push your service description, they expect it to be one of the services mentioned on this list. Extending it would make it nonstandard.
Finally, I found something called seap (SErvice Announcement Protocol). It's old, it's rickety, the source may be propriety, it's written in C and Perl, it's a kludge, but it seems to do what you want, kind-of.
It seems like pushing a service announcement pulse is such an application-specific and trivial problem, that almost nobody has considered solving the general case.
My advice? Read the protocols and sources mentioned above for inspiration (I'd start with seap), and then write, implement, and publish a generic (probably xml-based) protocol yourself. All the existing ones seem to be either application-specific, incomprehensible, or a kludge.
Basically, you can write it yourself though I am not aware if anyone has one for public (I wrote one over 10 yrs ago, but for a company).
database (TableCols: auto-counter, svr_name, svr_ip, check_in_time, any-other-data)
code to receive heartbeat (http://<you-app.com>?svr_name=XYZ&svr_ip=P.Q.R.S)
code to list out servers within certain check_in_time
code to do some housecleaning once a while (eg: purge old records)
To send a heartbeat out, you only need to send a http:// call, on Linux use wget* with crontab, on windows use wget.exe with task scheduler.
It is application specific, so even if you wrote one yourself, others can't use it without modifying the source code.
What tools will come in handy to debug and monitor SaaS services built on WCF in production environment ?
FYI - No access to the actual server whatsoever. No remoting in, and no access to the file system.
There are dozens of 'dotcom-monitors' (eg site24x7.com) but they can only monitor parameters that are publicly available, like site uptime, response times etc.
If you want to monitor memory usage and other parameters known only from 'inside', then you have two choices: either install some monitoring agent on a server (in most cases it would be a pain).
You can also send 'signals' from your code to some external event handling and notification service. I recommend AlertGrid (http://alert-grid.com) for the latter purpose it is very flexible and extremely easy to integrate.
AlertGrid doesn't require installation, access to the file system etc. it just gathers data you send and allows to build some notification rules. Examples:
you can send some parameter like memory usage and built rule 'if memory_usage > threshold -> send SMS to admin'
you can send data related to your applicatioin. If you have application proceeding orders, you can send number of processed orders in the signal and build notification rules around that
If you have some logic trigerred periodically (cron, windows service) you can send signal each time your logic is executed to check if it is executed on a scheduled basis.
(I am a developer in AlertGrid's team, in case of any question, please feel free to ask.)
What exactly do you want to monitor? If you only care about availability then good old ping might be enough :)
I'm playing around with windows azure and I would like to build a clouded server application that receives messages from many different clients, such as mobile and desktop.
I would like to build the client so that they work while in "offline-mode", i.e. I would like the client to build up a local queue of messages that are sent to the azure server as soon as they get online.
Can I accomplish this using wcf and/or azure queing mechanism, so that I don't have to worry about whether the client is online or offline when I write the code?
You won't need queuing in the cloud to accomplish this. For the client app to be "offline enabled" you need to do queuing on the client. For this there are many options, a local database, xml files, etc. Whenever the app senses network availability you can upload your queue to Azure. And yes, you can use WCF for that.
For the client queue/sync stuff you could take a look at the Sync Framework.
I haven't found a great need for the queue so far. Maybe it's just that I'm not seeing it in my app view. Could also be that the data you can store in the queue is minimal. You basically store short text strings (like record ids), and then you have to do something with the ID when you pull it from the queue, such as look it up, delete it, whatever.
In my app, I didn't use the queue at all, just as Peter suggests. I wrote directly to table storage (accessed via it's REST interface using StorageClient) from the client. If you want to look at a concrete example, take a look at http://www.netalerts.mobi/traffic. Like you, I wanted to learn Azure so I built a small web site.
There's a worker_role that wakes up every 60 seconds. Using one thread, it retrieves any new data from it's source (screen scraping a web page). New entries are stored directly in table storage (no need for a queue). Another thread deletes entries in table storage that are older than a specified threshold (there's no issue with running multiple threads against table storage). And then I'm working on the third thread which is designed to send notifications to handheld devices.
The app itself is a web_role, obviously.