Skip to main content

Creating VM-II

Yeah probably if somebody 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 from conf file
its enough for the conf file to have

lxc.utsname = beta = veth = up = 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 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

Now you should be able to ping 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 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 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 should work. 


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.

More on Memory

 A post almost after 2 years!!! One common question I get asked is, "what is the reference I follow for troubleshooting an issue at hand". I would not be able to give an answer to the question directly as most of the times, I won't have even a single reference material handy. It's not a self boasting article. It's an article describing how knowledge we gather at random places help during an issue. Let's dissect a memory usage issue in Linux I faced recently and see how the triage shaped up. One of our processes was getting repeated ENOMEM when it was trying to call malloc for some reason despite the box had plenty of unused RAM. Lets see how the triage went through I didn't understand in my Operating systems course what a virtual memory is. I did convincing myself that virtual memory is physical memory + swap(in a way correct but not completely) I attended an interview in 2013, where the Director of the division asked me when you do malloc do you get physi

Lessons from Memory

Started debugging an issue where Linux started calling OOM reaper despite tons of memory is used as Linux cached pages. My assumption was if there is a memory pressure, cache should shrink and leave way for the application to use. This is the documented and expected behavior. OOM reaper is called when few number of times page allocation has failed consequently. If for example mysql wants to grow its buffer and it asks for a page allocation and if the page allocation fails repeatedly, kernel invokes oom reaper. OOM reaper won't move out pages, it sleeps for some time and sees if kswapd or a program has freed up caches/application pages. If not it will start doing the dirty job of killing applications and freeing up memory. In our mysql setup, mysql is the application using most of the Used Memory, so no other application can free up memory for mysql to use. Cached pages are stored as 2 lists in Linux kernel viz active and inactive. More details here