I've set up two Mail Servers. Everything works great with replication between them.
But in my scenario there is the following problem: server1 is a powerfull machine, server2 is only a small container (just for failover).
There are for clients A DNS-Records like imap.server.xy which point to both servers.
I want the clients to use primarily the strong machine. I have tried adding to the A-Record for the strong server a priority.
Unfortunately this doesn't work, clients don't prefer the stronger server, they also use the small container.
Is there any way to use priority in A-Records with DNS-Round Robin?
Thank you!
Related
Problem:
I have an AWS EC2 instance running FreeBSD. In there, I'm running a NodeJS TLS/TCP server. I'd like to create a set of rules (in my NodeJS application) to be able to individually block IP addresses programmatically based on a few logical conditions.
I'd like to run an external (not on the same machine/instance) firewall or load-balancer, that I can control from NodeJS programmatically, such that when certain conditions are given, I can block a specific remote-address(IP) before it reaches the NodeJS instance.
Things I've tried:
I have initially looked into nginx as an option, running it on a second instance, and placing my NodeJS server behind it, but after skimming through the NGINX
Cookbook
Advanced Recipes for High Performance
Load Balancing I've learned that only the NGINX Plus (the paid version) allows for remote/API control & customization. While I believe that paying $3500/license is not too much (considering all NGINX Plus' features), I simply can not afford to buy it at this point in time; in addition the only feature I'd be using (at this point) would be the remote API control and the IP address blocking.
My second thought was to go with the AWS/ELB (elastic-load-balancer) by integrating AWS' SDK into my project. That sounded feasible, unfortunately, after reading a few forum threads and part of their documentation (unless I'm mistaken) it seems these two features I need are not available on the AWS/ELB. AWS seems to offer an entire different service called WAF that I honestly don't understand very well (both as a service and from a feature-stand-point).
I have also (briefly) looked into CloudFlare, as it was recommended in one of the posts, here on Sackoverflow, though I can't really tell if their firewall would allow this level of (remote) control.
Question:
What are my options? What would you guys recommend I did?
I think Nginx provide such kind of functionality please refer to link
If you want to block an IP with Node TCP you can just edit a nginx config file and deny IP address.
Frankly speaking, If I were you, I would use AWS WAF but if you don’t want to use it, you can simply use Node JS
In Node JS You should have a global array variable where you will store all blocked IP addresses and upon connection, you will check whether connected host IP is in blocked IP variable. However there occurs a problem when machine or application is restarted, you will lose all information about blocked IP-s. So as a solution to that you can just setup Redis (It is key-value database but there are also other datatypes) DB and store blocked IP-s there. Inasmuch as Redis DB is in RAM all interaction with DB will be instantly and as long as machine or node is restarted, Redis makes a backup on hard drive and it syncs from it and continue to work in RAM with old databases.
With the DDOS attack on the Dyn DNS service last week, I lost a day of productivity. Can I set up a DNS service on my MacPro laptop?
I envision it just caching the DNS info from the usual servers. If they go down, it can use the reasonably current info stored locally, and I can keep working.
Is that possible?
You would be better off using a cloud-hosted linux instance and setting up something more reliable. Like BIND configured as a caching server. Here is some discussion of that: https://www.digitalocean.com/community/tutorials/how-to-configure-bind-as-a-caching-or-forwarding-dns-server-on-ubuntu-14-04
Doing this on a Mac OS X client would be kludgy and unreliable. If you do want to go that route, I wouldn't go much further than just adding some common ones to /etc/hosts -- which is straightforward to do, but not scalable at all.
OS X Server has some capabilities to run a DNS Caching Server, but I suspect you're not running that.
I have a slight problem bit of the back story. recently ive been trying to test out univention which is a linux distribution with the goal of being able to replace Microsoft active directory.
I tested it locally and all went reasonably well after a few minor issues i then decided to test it remotely as the company wants to allow remote users to access this so i used myhyve.com to host it and its now been setup successfully and works reasonably well.
however
my main problem is DNS based as when trying to connect to the domain the only way windows will recognize it is by editing the network adapter and setting ip v4 dns server address to the ip address of the server hosting the univention active directory replacement. although this does allow every thing to work its not ideal and dns look up on the internet are considerably longer. i was wondering if any one had any ideas or have done something similar and encountered this problems before and know a work around. i want to avoid setting up a vpn if possible.
after initially registering the computer on the domain i am able to remove the dns server address and just use a couple of amendments to the HOST file to keep it running but this still leads to having issues connecting to the domain controller sometimes and is not ideal. any ideas and suggestions would be greatly received.
.Michael
For the HOST entries, the most likely issue is, that there are several service records a computer in the domain needs. I'm not sure, whether these can be provided via the HOST file or not but you'll definitely have authentication issues if they are missing. To see the records your domain is using issue the following commands on the UCS system.
/usr/share/univention-samba4/scripts/check_essential_samba4_dns_records.sh
For the slow resolution of the DNS records there are several points where you could start looking. My first test would be whether or not you are using a forwarder for the web DNS requests and whether or not the forwarder is having a decent speed. To check if you are using one, type
ucr search dns/forwarder
If you get a valid IP for either of the UCR Variables, dns/forwarder1, dns/forwarder2 or dns/forwarder3, you are forwarding your DNS requests to a different Server. If all of them are empty or not valid IPs then your server is doing the resolution itself.
Not using a forwarder is often slow, as the DNS servers caching is optimized for the AD operations, like the round robin load balancing. Likewise a number of ISPs require you to use a forwarder to minimize the DNS traffic. You can simply define a forwarder using ucr, I use Google on IPv4 for the example
ucr set dns/forwarder1='8.8.8.8'
The other scenario might be a slow forwarder. To check it try to query the forwarder directly using the following command
dig univention.com #(ucr get dns/forwarder1)
If it takes long, then there is nothing the UCS server can do, you'll simply have to choose a different forwarder from the ucr command above.
If neither of the above helps, the next step would be to check whether there are error messages for the named daemon in the syslog file. Normally these come when you are trying to manually remove software or if the firewall configuration got changed.
Kevin
Sponsored post, as I work for Univention North America, Inc.
I want to know how to structure my NodeJS server.
I want to separate services proposed on my website to mount cluster in the future and to have many servers (each allowed to one special task).
Example :
The 'main' server which have one project : ExpressJS and Database
The 'communication server' which have one project : Chat + Forum
Others projects : For complex computing (generating chart / stats / emailing)
Could you explain me different approach for this type of complex website ?
Like Benjamin Gruenbaym said, the architecture belongs somewhere else.
If you are wondering about how to setup the applications on an individual server, there are a few things to keep in mind.
NodeJS runs in a single process, so it should ideally take up 1 core of the CPU. If you run a database on the same server, that is another core. So it may be fine to host all node applications on the same server, if it has a sufficient number of cores.
To run two different Node processes on the same machine, you simply start them one after another, but make sure that they listen on different ports.
To make sure that you can scale out your application later, it is important that you use domain names, instead of IP adresses when you identify your services to each other. So the nodeJS app should know about the database as mydatabase.mycompany.com, not as 192.168.1.10 or any other ip address. This will allow you to later move the database to another network address or to use a load balancer.
This is my first time building out something with multiple servers. I wanted to know if anyone could point me towards a guide for setting up a dev environment (windows) for a backend that will be set up on multiple servers ie one server for the API, one for another set of processes (ie file compression) and one for everything else.
Again, just trying to figure out if it's possible to set up a dev environment to test out the system on my local machine.
Thanks
You almost certainly want to run virtual machines (on something like VMWare or VirtualBox) to really test multi-machine stuff. However, I also develop for multiple machines every day (we have an array of app servers, an array of background worker servers, e-commerce servers, cache stores and front proxies—and I still just develop on one virtual machine that has all that stuff running on it. Provided you make hostnames and ports configurable for everything, there's not much difference between localhost port 9000 and some.server.tld port 8080. Actually running all the VMs on a single computer would likely be painful, both in terms of system resources and complexity.
There are tools to help with setting up VMs with similar or the same configurations too. Take a look at http://vagrantup.com/ and also http://babushka.me/.
Just my $0.02.