README.md

Reproducer of a slow push due to image complexity

Prerequisities

• Deploy 2 VMs with RHEL7.
• Install docker v1.8.2-10.el7 on both.
• Choose a machine hosting upstream docker registry. Let's call it RegistryNode.
• Let's call the other Client.
• Remember the IP or hostname of the RegistryNode

Setup

• Enable tcp port 5000 on RegistryNode.
• Copy setup-registry-host.sh to RegistryNode and run it.
• Copy setup-client-host.sh to Client and run it.
• Copy generate-load.sh to Client and run it.

Test

Now the interesting part. We've got two images of similar size:

1. $REGISTRY_NODE:5000/test/packed
2. $REGISTRY_NODE:5000/test/unpacked

The former has 3 layers, each containing just one file - a tarball. The latter has also 3 layers, each containing unpacked tarball of the first image.

Push without load

Compare the times of running following command without any load:

time docker push "$REGISTRY_NODE:5000/test/packed"
time docker push "$REGISTRY_NODE:5000/test/unpacked"

Time of the latter will be slightly bigger due to higher complexity of the layers.

# Important - re-deploy the registry on *RegistryNode* before re-runing or continuing with other test
docker stop test-registry
./setup-regisitry-host.sh

Push with load

Generate some load on the Client:

./generate-load.sh

Compare the times again:

time docker push "$REGISTRY_NODE:5000/test/packed"
time docker push "$REGISTRY_NODE:5000/test/unpacked"

This time the second push will be a lot slower.

generate-load.sh

#!/bin/bash

set -euo pipefail

CORES=`grep '^processor\s*:' /proc/cpuinfo | wc -l`
for i in `seq $CORES`; do
    dd if=/dev/zero of=/dev/null &
done

trap 'kill $(jobs -p)' EXIT
wait %%

setup-client-host.sh

#!/bin/bash
#
# Run as root.
# Requires docker to be installed and configured.
# This script installs upstream docker registry and runs it.

set -euo pipefail
IFS=$'\n\t'

USAGE="Usage: $0 <registry-host-name> <registry-port>"

if [[ $# -lt 2 ]]; then
    printf "%s\n" "$USAGE"
    exit 1
fi

IMAGES=(fedora centos ubuntu)
HOSTNAME="$1"
PORT="$2"

set -x

for img in "${IMAGES[@]}"; do
    docker pull docker.io/$img
done

tmp=`mktemp -d`
function finish {
  rm -rf "$tmp"
}
trap finish EXIT

pushd $tmp
    mkdir packed unpacked
    echo "FROM scratch" >unpacked/Dockerfile
    echo "FROM scratch" >packed/Dockerfile

    for img in "${IMAGES[@]}"; do
        mkdir "packed/$img" "unpacked/$img"
        cid=`docker run -d $img /bin/true`
        docker export -o "packed/${img}.tar" $cid
        tar -xf "packed/${img}.tar" -C "unpacked/$img"
        echo "ADD $img /$img" >>unpacked/Dockerfile
        echo "COPY $img.tar /$img.tar" >>packed/Dockerfile
    done

    for dir in packed unpacked; do
        docker inspect "$HOSTNAME:$PORT/test/$dir" >/dev/null && continue
        docker build -t $HOSTNAME:$PORT/test/$dir $dir
    done
popd

set +x

echo "Built images:"
docker images | egrep "$HOSTNAME:$PORT/test/(un)?packed"
echo

set -x
docker history "$HOSTNAME:$PORT/test/unpacked"
docker history "$HOSTNAME:$PORT/test/packed"

setup-registry-host.sh

#!/bin/bash

# Run as root.
# Requires docker to be installed and configured.
# This script installs upstream docker registry and runs it.

set -euo pipefail

docker pull docker.io/registry:2.2.1
docker run -it --name test-registry --rm docker.io/registry:2.2.1 &