CS695-Assignment-3

Programming Assignment 3 - Build your own container using Linux namespaces and cgroups
Problem Statement PDF (https://www.cse.iitb.ac.in/~cs695/pa/pa3.html)
Demo Video

Solution Details and Steps

Prerequisites
1. Root filesystem rootfs.tar.gz from https://github.com/ericchiang/containers-from-scratch/releases/download/v0.1.0/rootfs.tar.gz
```
cd src
wget https://github.com/ericchiang/containers-from-scratch/releases/download/v0.1.0/rootfs.tar.gz
```

Steps to run/test the program

NOTE: all the below commands need to be executed using root privileges
Change the working directory
```
cd src
```

Counter and Root filesystem name generating functions

# Variable: v_NUM
function f_update_counter() { 
    if [[ -f 'CONTAINER_NUMBER.txt' ]]; then
        v_NUM=$(cat 'CONTAINER_NUMBER.txt')
    else
        v_NUM=0
    fi

    v_NUM=$(($v_NUM + 1))
    echo $v_NUM > 'CONTAINER_NUMBER.txt'       
    echo "v_NUM = ${v_NUM}"
}

# Variable: v_NEW_DIR_NAME
function f_get_new_dir_name() {
    while true; do
        f_update_counter
        
        v_NEW_DIR_NAME="rootfs_${v_NUM}"
        if [[ -d "${v_NEW_DIR_NAME}" ]]; then
            echo "WARNING: Directory already exists: '${v_NEW_DIR_NAME}'"
        else
            echo "Using Directory Name: '${v_NEW_DIR_NAME}'"
            break
        fi       
    done
}

Extract the root filesystem rootfs.tar.gz

f_get_new_dir_name

mkdir "${v_NEW_DIR_NAME}_tmp"
tar --verbose --gzip --extract --file "rootfs.tar.gz" -C "${v_NEW_DIR_NAME}_tmp"  # OR, tar -vzxf "rootfs.tar.gz"
mv "${v_NEW_DIR_NAME}_tmp/rootfs" "${v_NEW_DIR_NAME}"
rmdir "${v_NEW_DIR_NAME}_tmp"

# The below lines will create "random" and "urandom" files inside the "${v_NEW_DIR_NAME}/dev"
# directory. This is necessary because python inside this root filesystem needs these files.
mknod -m 0666 "${v_NEW_DIR_NAME}/dev/random" c 1 8
mknod -m 0666 "${v_NEW_DIR_NAME}/dev/urandom" c 1 9
chown root:root "${v_NEW_DIR_NAME}/dev/random" "${v_NEW_DIR_NAME}/dev/urandom"

Create CPU and Memory cgroup (OPTIONAL)

# NOTE: can view the CGROUP a process is in: 
#       System Monitor > Processes > Right Click on Process Name > Scroll Down to see "Control Group"

# REFER: https://man7.org/linux/man-pages/man7/cgroups.7.html

# REFER: https://www.kernel.org/doc/Documentation/scheduler/sched-bwc.txt
CGROUP_CPU_NAME="cs695cpu"
mkdir "/sys/fs/cgroup/cpu/${CGROUP_CPU_NAME}"
# With 1 second period, 0.5 second quota will be equivalent to 50% of 1 CPU
echo "1000000" > "/sys/fs/cgroup/cpu/${CGROUP_CPU_NAME}/cpu.cfs_period_us"
echo "500000" > "/sys/fs/cgroup/cpu/${CGROUP_CPU_NAME}/cpu.cfs_quota_us"

# REFER: https://www.kernel.org/doc/Documentation/cgroup-v1/memory.txt
CGROUP_MEMORY_NAME="cs695mem"
mkdir "/sys/fs/cgroup/memory/${CGROUP_MEMORY_NAME}"
# set limit of memory usage      = 16 MB = 16 * 1024 * 1024 = 16777216
# set limit of memory+Swap usage = 24 MB = 24 * 1024 * 1024 = 25165824
echo "16777216" > "/sys/fs/cgroup/memory/${CGROUP_MEMORY_NAME}/memory.limit_in_bytes"
echo "25165824" > "/sys/fs/cgroup/memory/${CGROUP_MEMORY_NAME}/memory.memsw.limit_in_bytes"

# --------------------

# TESTING
echo $$ > "/sys/fs/cgroup/cpu/${CGROUP_CPU_NAME}/cgroup.procs"
echo $$ > "/sys/fs/cgroup/memory/${CGROUP_MEMORY_NAME}/cgroup.procs"

# Testing of CPU, view the CPU usage via the System Monitor
while true; do
  a=$((12345*12345))
done
while true; do a=$((12345*12345)); done &  # background process

# Testing of Memory Limits, view the Memory usage via SystemMonitor
# This will abort the process in the 13th iteration for 16 MB (RAM), 24 MB (RAM + SWAP)
# 12th iteration = ~10 MB, 13th iteration = ~28 MB, 14th iteration = ~83 MB, 15th iteration = ~247 MB
# REFER: https://stackoverflow.com/questions/40888164/c-program-crashes-with-exit-code-9-sigkill
a="123"
for i in {1..12}; do
  echo $i
  a="${a}${a}${a}"
  sleep 1
done
a="${a}${a}"

Network Namespace creation and initialization (OPTIONAL)

# NOTE: internet access MAY not work (NOT tested)
# NOTE: if this step is not performed, then local client server program will not work
NETWORK_NAMESPACE_NAME="cs695netns${v_NUM}"
v_VETH0="cs695vethA${v_NUM}"
v_VETH1="cs695vethB${v_NUM}"

# Create a network namespace
ip netns add "${NETWORK_NAMESPACE_NAME}"
# Turn the "lo" interface up
ip netns exec "${NETWORK_NAMESPACE_NAME}" ip link set dev lo up
# Create virtual ethernet A and B
ip link add "${v_VETH0}" type veth peer name "${v_VETH1}"
# veth B to namespace
ip link set "${v_VETH1}" netns "${NETWORK_NAMESPACE_NAME}"

# Find NEW IP address based on ${v_NUM}
v_VETH0_IP="$(python3 IPGenerator.py ${v_NUM} a)"
v_VETH1_IP="$(python3 IPGenerator.py ${v_NUM} b)"

# IMPORTANT: if below checks give error, then set any unused IP address manually using:
# v_VETH0_IP="10.0.0.1/24"
# v_VETH1_IP="10.0.0.2/24"
if [[ $v_VETH0_IP == ERROR* ]]; then echo -e "WARNING: do NOT proceed\n${v_VETH0_IP}"; fi
if [[ $v_VETH1_IP == ERROR* ]]; then echo -e "WARNING: do NOT proceed\n${v_VETH1_IP}"; fi

ifconfig "${v_VETH0}" "${v_VETH0_IP}" up
ip netns exec "${NETWORK_NAMESPACE_NAME}" ifconfig "${v_VETH1}" "${v_VETH1_IP}" up

Compile and Execute the container shell

# CGROUP_CPU_PATH is relative path to "/sys/fs/cgroup/cpu/"
# CGROUP_MEMORY_PATH is relative path to "/sys/fs/cgroup/memory/"
make all
./MyContainer.out <ROOT_FS_PATH> <HOSTNAME> \
    <CGROUP_CPU_PATH> <CGROUP_MEMORY_PATH> <NETWORK_NAMESPACE_NAME> <MOUNT_DIR_PATH>

make debug
./MyContainer_debug.out \
    "${v_NEW_DIR_NAME}" \
    "hostname-${v_NEW_DIR_NAME}" \
    "${CGROUP_CPU_NAME}"         \
    "${CGROUP_MEMORY_NAME}"      \
    "${NETWORK_NAMESPACE_NAME}"     \
    "custom_mount_folder"

Clean the binaries generated
```
make clean
```

References

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CS 695 - Assignment 3 - Container

linux-container

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