Wednesday, May 25, 2016

[Proxy ARP] What is Proxy ARP?

Why I mention Proxy ARP is because in OpenStack environment, this function exists in FIP namespace with DVR enabled. The way to check whether the FIP namespace's Proxy ARP enabled is here:
# ip netns exec fip-545b57e2-0fa5-46da-89a2-591f7a5474ce cat /proc/sys/net/ipv4/conf/fg-2f3f4992-23/proxy_arp

We also can see the arp and ip mapping:
# ip netns exec fip-545b57e2-0fa5-46da-89a2-591f7a5474ce ip neighbor dev fpr-6ddabb95-1 lladdr 42:72:88:ca:07:72 STALE

The following is the explaination about Proxy ARP

Occasionally, an IP network must be split into separate segments. Proxy ARP can be used for increased control over packets exchanged between two hosts or to limit exposure between two hosts in a single IP network. The technique of proxy ARP is commonly used to interpose a device with higher layer functionality between two other hosts. From a practical standpoint, there is little difference between the functions of a packet-filtering bridge and a firewall performing proxy ARP. The manner by which the interposed device receives the packets, however, is tremendously different.

Example 2.10. Proxy ARP Network Diagram

The device performing proxy ARP (masq-gw) responds for all ARP queries on behalf of IPs reachable on interfaces other than the interface on which the query arrives.

FIXME; manual proxy ARP (see also Section 9.3, “Breaking a network in two with proxy ARP”), kernel proxy ARP, and the newly supported sysctl net/ipv4/conf/$DEV/medium_id.

For a brief description of the use of medium_id, see Julian's remarks.

FIXME; Kernel proxy ARP with the sysctl net/ipv4/conf/$DEV/proxy_arp.

Tuesday, May 10, 2016

[Docker] the first experience with building docker image

It is essential to look for the docker image first if you need some services or functions running on docker container. But, once you want to customize it, you probably need to build your own docker image. The official document gives you a very complete description for you to do so. Please refer to this
The following command list are my steps to build a customized Drupal docker image.
The are two ways to build your own image:

1. Updating and committing an image

First, it would be better to have a Docker Hub account like this:

Second, to create a repository for your docker image.

If it's done, you can see this:

So, we can continue to the next step.
# Download the offical Drupal docker image
$ docker search drupal
$ docker pull drupal
$ docker images

# Create a container and update it ( be aware of the follwing parameters )
$ docker run -i -t --name danny_drupal -p 8000:80 drupal /bin/bash
  -i, --interactive               Keep STDIN open even if not attached
  -t, --tty                       Allocate a pseudo-TTY
  -p, --publish=[]                Publish a container's port(s) to the host

# From now on, you can go anything for your container
root@2a0849519c71:/var/www/html# apt-get update
root@2a0849519c71:/var/www/html# apt-get install openssh-server cloud-init -y
root@2a0849519c71:/var/www/html# exit

# To commit my changes
$  docker commit -m "Added my services" -a "teyenliu" \
danny_drupal teyenliu/drupal:v1

# Have to login docker before you push your change
$ docker login --username=teyenliu
$ docker push teyenliu/drupal

# Now it is successful to push your own drupal image and you also can see it on docker hub:

# To test your own drupal image:
$ docker run --name danny_drupal -p 8000:80 -d teyenliu/drupal:v1

# To check if the container is running
$ docker ps

# Open your browser with

2. Buidling an image from Dockerfile

$ vim Dockerfile
# This is a comment
FROM drupal:latest
RUN apt-get update && apt-get install -y git
RUN apt-get install -y openssh-server
RUN apt-get install -y cloud-init
$ docker build -t teyenliu/drupal:v2 .
$ docker push teyenliu/drupal:v2

# The drupal repository will append the image of tag:v2

P.S: If you want to put the docker image to OpenStack Glance for further using, here is an example command:
$ docker save teyenliu/drupal | glance image-create --container-format docker --disk-format raw --name teyenliu/druapl

Tuesday, May 3, 2016

[Python] Problem with Python logging RotatingFileHandler in Django website

If seeing the log files are not rotated properly or correctly in Django web site, you most likely encounter the problem as the following article described:

Problem with Python logging RotatingFileHandler in Django website
"The log is done via RotatingFileHandler which is configured with 10 log files, 1000000 byte each. The log system works, but this are the log files I get:
-rw-r--r-- 1 apache      apache          83 Jul 23 13:30 hr.log
-rw-r--r-- 1 apache      apache      446276 Jul 23 13:03 hr.log.1
-rw-r--r-- 1 apache      apache      999910 Jul 23 06:00 hr.log.10
-rw-r--r-- 1 apache      apache         415 Jul 23 16:24 hr.log.2
-rw-r--r-- 1 apache      apache      479636 Jul 23 16:03 hr.log.3
-rw-r--r-- 1 apache      apache         710 Jul 23 15:30 hr.log.4
-rw-r--r-- 1 apache      apache      892179 Jul 23 15:03 hr.log.5
-rw-r--r-- 1 apache      apache         166 Jul 23 14:30 hr.log.6
-rw-r--r-- 1 apache      apache      890769 Jul 23 14:03 hr.log.7
-rw-r--r-- 1 apache      apache      999977 Jul 23 12:30 hr.log.8
-rw-r--r-- 1 apache      apache      999961 Jul 23 08:01 hr.log.9
As you can see it is a mess. Last log has been written to file hr.log.2 (Jul 23 16:24) instead of hr.log"

I did some survey and found the root cause is in here:
RotatingFileHandler bugs/errors and a general logging question
"The logging system is thread-safe but not safe
against multiple processes (separate Python instances) writing to the
same file. It certainly sounds like you need a scalable solution - and
having each script send the events to a network logging server seems a
good way of handling the scalability requirement. "

    These words above remind me a lot about the importance of synchronization when using multi-threading and multi-process. Also, scaling is another important item that a lot of people don't care. I want to highlight that we should be vigilant about these.

So, it is not your fault. Don't blame yourself. ( Sorry, I am kidding you ... )
Here is one solution for this issue. Please check out the following link ( it's written in Chinese ):

[Linux Bonding] 802.3ad bond interface has shown RX dropped packets

If someone uses Linux Bonding and finds some or a lot of RX dropped packets in bond interface, please ignore these dropped packet message because of the following informations:

1. Linux Bonding and Single Nic with 1GE switch are no difference in packet loss
I use iperf tool with UDP to test packet drop and jitter and the result shows that there are no difference of packet loss between linux bonding and single nic.

2. Bond0 RX packet dropped is not a bug.
Please check out this:
This is related to the bonding mode and _not_ a bug. The bonding module will drop duplicate frames received on inactive ports, which is normal behavior. [0] Overall the packets should be getting into the machine without problems since they are received on the active slave. To confirm this do the following

1) Check dropped packets from all interfaces. So if eth0/eth1 are connected to bond0, we may see dropped packets for bond0 and eth0, but not for eth1. This depends on which interface is the active interface. This can be checked using the following:
cat /sys/class/net/bond0/bonding/active_slave

So if the active_slave isn't dropping packets, and the inactive slave is dropping packets this is normal in 'active-backup' mode (or any mode where there is an inactive slave).

2) If we want both interfaces to not drop packets we can use 'all_slaves_active' bonding module parameter [0].
cat /sys/class/net/bond0/bonding/all_slaves_active, it should default to 0 which means drop frames on the inactive slave.

If we set this to 1, we will no longer drop frames:
echo 1 | sudo tee /sys/class/net/bond0/bonding/all_slaves_active
3. This article suggests to turn off rp_filter ( could reduce RX dropped )
echo net.ipv4.conf.all.rp_filter=0 >> /etc/sysctl.conf
echo net.ipv4.conf.default.rp_filter=0 >> /etc/sysctl.conf
echo net.bridge.bridge-nf-call-iptables=1 >> /etc/sysctl.conf
echo net.ipv4.ip_forward=1 >> /etc/sysctl.conf
sysctl -p
What is reverse path filtering?

Reverse path filtering is a mechanism adopted by the Linux kernel, as well as most of the networking devices out there to check whether a receiving packet source address is routable.

So in other words, when a machine with reverse path filtering enabled recieves a packet, the machine will first check whether the source of the recived packet is reachable through the interface it came in.

If it is routable through the interface which it came, then the machine will accept the packet
If it is not routable through the interface, which it came, then the machine will drop that packet.

Other References: