Exam Question: You're using an external API, where the URL changes frequently. Which architecture is suited the best to solve this problem, without ever-changing the code for the program again?
I recently took an exam and there was this task to which i still cannot figure out the appropriate answer.The architectures mentioned in the lecture were P2P, C/S and SOA.
If anyone has a clue... Thanks!
I think the answer is p2p. In a Peer-to-peer network, computers advertise their services capabilities on the network. A changing URL would not be a problem, as the new URL is published to the network automatically and picked up by the consumers of the API.
In SOA and Client/Server the consumers of the API have no means to know about a change in the API URL.
Related
I am new to this, what is a best approach to implement microservices?
I found fw like seneca but it is little bit confusing...
Is there any tut how to create jwt auth, mongodb and other staff in microservices?
Take a look on Docker.
With docker-compose you can play with several services with an easy integration without worrying about the IP addresses to connect them.
Also if you add nginx to your stack, it's gonna be very easy to scale those services, there are several videos and tutorials that you can lookup to help you get started.
I've heard aboutseneca, but I haven't used, I think you shouldn't depend on a specific framework because one of the ideas behind of Microservices is the low coupling.
To make the jump into the real micro-services world is not trivial. It's not about plumbing some APIs, but a radical change in architecture thinking that, well, at the beginning will make you a bit uncomfortable (e.g. every service with its own database) :)
The best book I have read so far about micro-services is The Tao of Microservices, by Richard Rodger the author of Seneca himself. It exposes very well the shift from monolithic and object-oriented software towards micro-services.
I have personally struggled a bit with Seneca because of the average quality of documentation (inconsistencies, etc...). I would rather recommend Hemera, which took its inspiration from the message-pattern approach from Seneca, but is better documented and much more production-ready.
1) Build services and deploy it with Docker Containers
2) Let them communicate via gRPC coz it is really fast for inter services communication.
3) Use error reporter like Bugsnag or Rollbar. Error reporting is really important to catch error quickly.
4) Integrate tracing using opentracing or opencensus. Tracing is important too because it will be so hard to monitor all microservices with logs only.
I need a way for my web application to send push-notifications to the client side. Realtime is not a strong requirement, near-realtime is okay. I don't need anything fancy, just sending a string to the client every now and then, nothing more. What's really important is that the solution must be very simple and low-profile (performance-wise mainly). Could you give me advice on which framework to use?
Many people would say SignalR hands down, but I'm not sure about the performance part. It is not disqualified, I'll tell about my doubts below, and I'm also interested about any insights you may have about this, but the main question stays what I wrote above.
I read this article recently. What it provides is a long-running request pattern with only a few classes, a little IIS & async magic and nothing more. Even if you have an IIS connection limit of 200, it will barely use up any of those connections. Compared to this, SignalR is as complex and heavy-weight as a nuclear power plant. It comes with half a dozen different DLL's (like OWIN, which I haven't heard about before, and even after a bit of Googling, I can't figure out what it is). The performance wiki page of SignalR starts by suggesting to increase your concurrent request limit to a ridiculous amount. So I'm guessing it's not using the aforementioned "trick". I'm not exactly sure how bad that is, but in the light of that article, it doesn't sound good.
If you really want to push messages to the client, SignalR approach is very good. As far as I know it works with web-sockets. Try to digg this way. Here is some article for the beginning:
http://blogs.msdn.com/b/youssefm/archive/2012/07/17/building-real-time-web-apps-with-asp-net-webapi-and-websockets.aspx.
For mobile apps I would use great library PushSharp. https://github.com/Redth/PushSharp
With help of PushSharp you can send notifications to any mobile app: WindowsPhone, IOS, Android, Blackberry etc.
Please note: sending push notification differs from platform to platform.
Keep in mind approach with pinging server all the time and checking for new messages. It is probably the easiest way.
I use SignalR and toastr.js. SignalR can scale to thousands of connections. There are also native SignalR clients for iOS and Android (check out Signalr-ObjC).
Since noone answered about the resource requirements and my doubts about SignalR, which was the key question here, I'm accepting this as an answer: http://www.codeproject.com/Articles/27107/Scalable-COMET-Combined-with-ASP-NET .
I have a fairly complex windows service (written in .net 4) with several sub systems that run in parallel.
I have implemented pretty good logging throughout, but I'm feeling I'm needing more info about what each subsystem is currently doing. This would be very useful for times that I need to stop the service for upgrade/bug fixes.
It would be nice to have a gui app that will show me the status for each part of the application that I'm interested in. I've had some ideas for how I'm going to do this, but I'd like to hear some others' ideas as well.
I'm interested in a solution that would be easy to plop down in a future windows service and I'm not looking for anything very complex.
Are there any tools for this sort of thing?
Have you done this yourself?
What about interprocess communication?
Since Windows services can no longer interact with the user session, you'll need to have a separate application that does the interacting for you. Based on the details of your question, I think you understand this.
The big question is how to facilitate the communication between your Windows service and the application. There are all kinds of approaches - shared memory, socket, pipe, remoting, etc. What I have used successfully is WCF. If your UI is going to reside on the same machine as the service, use the NetNamedPipeBinding. If you ever need access from a remote machine, you can change to the NetTcpBinding. I've found this flow chart helpful in binding selection.
.
If you're looking for a more formal framework approach that just straight WCF, have a look at Juval Lowy's Publish-Subscribe WCF Framework, which is described in pretty good detail in this MSDN article. The code is available to look at via the article, or you can download the source and example from Lowy's website here. Go to the Downloads section, filter by the Discovery category, and you'll see it there.
I Program my local schools program launcher which allows students to get on the internet with an randomly generated key provided by a teacher. This is done by changing the proxy in Internet explorer to the one needed for the internet and the wb filter.
With the schools website and learning resources gradually moving to offsite hosting the internet key is needed for the students to access them. What the school would like is a way to enable these websites without unblocking the rest of the internet unless the internet key is given to the student.
The two ways ive come up with doing this by googleing is to block all websites in IE content adviser exept those that are allowed wthout the key. Or to create anouther proxy in delphi which the program can make ie point to and will only allow certain websites through to the real proxy.
I am reasonble fluent in simple delphi functions with an a level in computing but dont have a clue where to start with this and would appreciate any help.
Don't go through the DIY path - use a proxy with blacklist/whitelist functionalities, you can also set up a "transparent proxy" through which all internet traffic is routed and doesn't require to setup the proxy in browsers. You can also use proxy authentication to setup who can access what.
In Delphi you will end up to write a proxy with the same functionalities. If you don't have a very good rason to write your own proxy, it's far better to go through an already existing solutions, which also is already tested by a lot of users. There are commercial and opensource/free ones.
If you really like to write a proxy in Delphi:
A good knowledge of how TCP, HTTP(S), and a proxy works is required.
The application needs to be a service, and should be robust or accessing the Internet may be become impossible.
The application will have to serve concurrent requests, thereby it needs to be multithreaded (Indy offers a basic HTTP proxy component - how well it scales I do not know, and it implements basic features only).
If you need authentication, knowledge of authentication methods and if integrated authentication is needed, how Windows auhtentication works.
It should be tested with all the browser type used.
Although a very interesting app to write from scratch if you liked to learn about that all, if you have a "business need" it's better to use an already existing one.
+1 and the proxy may cache some of the Internet resources, so the whole Internet experience will be smoother with such a tool.
I'll recommend using a linux box (some old PC can be revamped into this) with Squid, just to separate your students network to the Internet. There is a lot of info on the Internet about that, and also dedicated linux distributions: a lot of schools around the world had the same problem!
OpenDNS is the best place to start. Put that up, set all PCs to use it, and that'll take care of most of your problems.
Closed. This question is opinion-based. It is not currently accepting answers.
Want to improve this question? Update the question so it can be answered with facts and citations by editing this post.
Closed 7 years ago.
Improve this question
I was recently approached by a network-engineer, co-worker who would like to offload his minor network admin duties to a junior-level helpdesk tech. The specific location in need of management acts as an ISP for tenants on its single-site property, so there's a lot of small adjustments being made on a daily basis.
I am thinking it would be helpful to write him a winform app to manage the 32 Cisco devices, on-site. I'd like to initially provide functionality which could modify access control lists, port VLAN assignments, and bandwidth limitations per VLAN... adding more to the list as its deemed valuable.
My initial thought was to emulate a telnet session with the network device; utilizing my network-engineer's familiarity with the command-line / IOS interaction. Minimal time would be required to learn Cisco IOS conventions, myself.
Though while searching for solutions, it appears that most people favor SNMP. That, or, their specific circumstances pushed them in the direction of SNMP.
I wanted to know if I've overlooked an obvious benefit of SNMP. Should I be using SNMP? Why or why not?
SNMP is great for getting information out of a Cisco device, but is not very useful controlling the device. (although technically, you can push a new config to a Cisco IOS device using a combination of SNMP and TFTP. But sending a whole new config is a pretty blunt instrument for controlling your router or switch).
One of the other commenters mentioned the Cisco IOS XR XML API. It's important to note that the IOS XR XML API is only available on devices that run IOS XR. IOS XR is only used on a few of Cisco's high end carrier class devices, so for 99% of all Cisco routers and switches the IOS XR XML API is not an option.
Other possibilities are SSH or HTTP (many Cisco routers, switches, AP, etc. have an optional web interface). But I'd recommend against either of those. To my knowledge, the web interface isn't very consistent across devices, and a rather surprising number of Cisco devices don't support SSH, or at least don't support it in the base license.
Telnet is really the only way to go, unless you're only targeting a small range of device models. To give you something to compare against, Cisco's own CiscoWorks network management software uses Telnet to connect to managed devices.
I wouldn't use SNMP, instead look at a little language called 'expect'. it makes for a very nice expect/response processor for these routers.
I have done a reasonable amount of real world SNMP programming with Cisco switches and find Python on top of Net-SNMP to be quite reasonable. Here is an example, via Google books, of uploading a new Cisco configuration via Net-SNMP and Python: Cisco Switch Upload via Net-SNMP and Python. I should disclose I was the co-author of the book referenced in the link.
Everyone's milage may vary, but I personally do not like using expect, and prefer to use SNMP because it was actually designed to be a "Simple Network Management Protocol". In a pinch, expect is ok, but it would not be my first choice. One of the reasons some companies use expect is that a developer just gets used to using expect. I wouldn't necessarily chock up bypassing SNMP just because there is an example of someone automating telnet or ssh. Try it out for self first.
There can be some truly horrible things that happen with expect, that may not be obvious as well. Because expect waits for input, under the right conditions there be very subtle problems that are difficult to debug. This doesn't mean a very experienced developer can't develop reliable code with expect, but it something to be aware of as well.
One of the other things you may want to look at is an example of using the multiprocessing module to write non-blocking SNMP code. Because this is my first post to stackoverflow I cannot post more then one link, but if you google for it you can find it, or another one on using IPython and Net-SNMP.
One thing to keep in mind when writing SNMP code is that it involves reading a lot of documentation and doing trial and error. In the case of Cisco, the documentation is quite good though.
SNMP isn't bad but it may not be able to do everything you need it to do. Depending on the library you use and how it hides the details of interacting with SNMP you may have a hard time finding the correct parts of the MIB to change and even knowing what or how to change them to do what you want.
One reason not to use SNMP is that you can do all the configuration you need using the IOS XR XML API. It could be a lot easier to bundle up the commands you want to send to the devices using that than to interact with SNMP.
I've found SNMP to be a pain for management. If you just need to grab a little data it's great; if you need to change things or use if heavily it can be very time consuming. In my case I'm comfortable with the CLI so a Telnet approach works well. I've written some Python scripts to perform administrative tasks on various pieces of network gear using Telnetlib
SNMP has quite a significant CPU hit on the devices in question compared to telnet; I'd recommend telnet wherever possible. (As stated in a previous answer, the IOS XR XML API would be nice, but as far as I know IOS XR is only deployed on high-end carrier grade routers).
In terms of existing configuration management systems, two commercial players are HP Opsware, and EMC Voyence. Both will probably do what you need. I'm not aware of many open source solutions that actually support deploying changes. (RANCID, for example, only does configuration monitoring, not pre-staging and deploying config changes).
If you are going to roll your own solution, one thing I would recommend is sitting down with your network admin and coming up with a best-practice deployment model for the service he's providing (e.g. standardised ACL, QoS queue, and VLAN names; similar entries in ACLs that have the same function for different customers, etc.). Ensure that all the existing deployed config complies with this BP before you start your design, it will make the problem much more manageable. Best of luck.
Sidenote: before you reinvent the wheel writing another service provisioning system/network management system, try looking for existing ones. I know quite a lot of commercial solutions of various degrees of flexibility/functionality, but I am sure there are quite a lot opensource ones.
Cisco has included menu options for helpdesk applications. Basically you telnet to the box and it presents a nice clean menu (press 1, 2, 3). For more info check this link:
http://www.cisco.com/en/US/docs/ios/12_2/configfun/command/reference/frf001.html#wp1050026
Another vote for expect.
Also, you don't want to allow configuration of your firewalls via either telnet or SNMP - ssh is the only way to go. The reason is that ssh encrypts its payload, and will not expose the privileged management credentials to potential interception.
If for some reason you cannot use ssh directly, consider connecting up an ssh-enabled serial console server to the firewall's console port and configuring it that way.