Skip to main content

Networking In LXC

Had been trying to create multiple vm containers and make them reachable from the existing infrastructure switches.
So basically I will explain about my host system
My host system has two interfaces em1 and em2. em1 is attached to two vlan switch ports 211 and 103. So my interface looks like em1, em1.211, em1.103 and em2. em2 is reachable through my network.

1)Networking via veth:
I created a bridge interface br0 and attached it with em1.211 and em1.103. Now the containers use veth to bridge with br0 using veth pair. The usual flow of data will be

from outer world to container
em1.x(picks up in promisc mode)->br0->host veth pair->container

from outer world to host
em2(picks up packet as em1 has no ip)->host


2)Networking via macvlan:

Macvlan is a kernel feature which allows an interface to have multiple hw address and ip. So by default macvlan creates a new interface(virtual of an existing interface) with hw and ip addr pairs and then moves that interface to containers. If the link interface is given as br0 for config file with network type being vlan, the data flow here will be

from outer world to container
em1.x->br0->macvlan of container

But between containers communication as host do arp request for a container's ip when a request comes from another container in the network. But the requested container is behind the host and wont receive the arp packet. Communication between host and container is possible with the second interface of the host.

If macvlan type is made bridged, then containers packets with in themselves will be broadcasted to all macvlan interface and thereby making communication between containers possible. This method helps to get rid of veth pair interfaces on the host system, but the kernel needs to remember hardware address of all containers for inter vm communications

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