Skip to main content

Creating VM-II

Yeah probably if somebody http://blogs.eskratch.com/2012/10/create-your-own-vms-i.html tried this, you would have faced problems in network connectivity either to the host or vm. Documentation for LXC sucks. So lets quickly go through a series of steps to make host and container accessible

Requirements : The system should be connected to internet via ethernet. Use a ubuntu host

So lets use the dhcp proto to assign ips to our containers instead of static ips, remove lxc.network.pv4 from conf file
its enough for the conf file to have

lxc.utsname = beta
lxc.network.type = veth
lxc.network.flags = up
lxc.network.link = br0

Now create a bridge 
  brctl addbr br0

Attach the bridge with interface eth0
   brctl addif eth0
You should lose our internet connectivity bcoz during bridging eth0 enters promiscuous mode(where it reads all packets on network and forward to bridge, if the bridge knows the ip, forwards it, else drops it)
  ifconfig br0 up
create a lxc container of ubuntu
  lxc-create -n ub -f <config file as showed above> -t ubuntu
Start the container
   lxc-start -n ub

Since we didnt specify ip container will do a dhcp request within subnet(bridge interface)
Once the container comes up, you can try to ping 8.8.8.8 it should work
If it doesnot work add a route to default gateway(route add default gw <ip> dev eth0)
To find the ip of default gw, do a route -n on host(master) and find the gateway ip in the row corresponding to destination 0.0.0.0

Now you should be able to ping 8.8.8.8 despite the master is not connected to internet. Actually the problem is master has given up its ip, so its not receiving packets. 

To make the host connected to internet, 
  ifconfig eth0 0.0.0.0 up (taking the ip from eth0 as it is not considered in promiscuous mode)
  dhclient br0 -v(this helps us to understand dhcp process)
  ifconfig br0 up
br0 will have an ip now. Try to ping 8.8.8.8. If it fails, then the problem is with the route
Delete all routes with dev being eth0 using route del -n command(google will help you).
add default route with gw<ip> that you found earlier to dev br0
Now ping 8.8.8.8 should work. 


Comments

Post a Comment

Popular posts from this blog

How we have systematically improved the roads our packets travel to help data imports and exports flourish

This blog post is an account of how we have toiled over the years to improve the throughput of our interDC tunnels. I joined this company around 2012. We were scaling aggressively then. We quickly expanded to 4 DCs with a mixture of AWS and colocation. Our primary DC is connected to all these new DCs via IPSEC tunnels established from SRX. The SRX model we had, had an IPSEC throughput of 350Mbps. Around December 2015 we saturated the SRX. Buying SRX was an option on the table. Buying one with 2Gbps throughput would have cut the story short. The tech team didn't see it happening. I don't have an answer to the question, "Is it worth spending time in solving a problem if a solution is already available out of box?" This project helped us in improving our critical thinking and in experiencing the theoretical network fundamentals on live traffic, but also caused us quite a bit of fatigue due to management overhead. Cutting short the philosophy, lets jump to the story. ...
8 comments
Read more

LXC and Host Crashes

 We had set up a bunch of lxc containers on two servers each with 16 core CPUs and 64 GB RAM(for reliability and loadbalancing). Both the servers are on same vlan. The servers need to have atleast one of their network interface in promiscuous mode so that it forwards all packets on vlan to the bridge( http://blogs.eskratch.com/2012/10/create-your-own-vms-i.html ) which takes care of the routing to containers. If the packets are not addressed to the containers, the bridge drops the packet. Having this setup, we moved all our platform maintenance services to these containers. They are fault tolerant as we used two host machines where each host machine has a replica of the containers on the other. The probability to crash for both the servers at the same time due to some hardware/software failure is less. But to my surprise both the servers are crashing exactly the same time with a mean life time 20 days. We had to wake up late nights(early mornings) to fix stuffs that go...
Post a Comment
Read more

The FB outage

 This outage has caused considerable noise everywhere. It was quite discomforting for me because during the whole conversation nobody bothered to understand the gravity of the issue. I don't expect end users to understand the issue. But this is going to be a blogpost for all of those in the tech field, Such an event can happen how much ever chaos engineering, best of the tech jargon we implement in the stack To all my Site Reliability Engineer friends, Site Up is our first priority. I myself said many a times outage is news and SREs should prevent outage. But I'm afraid this is leading to a cult in the industry who despises outages and takes no learnings from it. I don't know what has happened in Facebook. I can explain a scenario which may or may not be right but that can definitely show the gravity of the issue. Let's draw a probable Facebook architecture Disclaimer I don't work at Facebook. So this might not be how facebook routes traffic. This is based on my exp...
2 comments
Read more