own_coreos_update

update

coreos update conf (/etc/coreos/update.conf, will install 723.3.0):
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SERVER=http://127.0.0.1/723.3.0/
GROUP=stable
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nginx conf:
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        error_page 405 =200 $uri;
        location / {
                root /home/coreos_updates/amd64-usr;
        }

        location /amd64-usr {
                root /home/coreos_updates;
        }
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bash script to download images and generate XML:
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#!/bin/bash

URL="http://127.0.0.1" 
VERSION="$1" 

if [ ! -d $VERSION ]; then
        mkdir -p $VERSION
fi

if [ ! -f $VERSION/update.gz ]; then
        wget -qP $VERSION https://update.release.core-os.net/amd64-usr/$VERSION/update.gz
fi

SIZE=$(stat -c %s ${VERSION}/update.gz)
SHA1_b64=$(echo -ne "$(echo -n $(sha1sum ${VERSION}/update.gz | awk '{print $1}') | sed -e 's/../\\x&/g')" | base64 )
SHA256_b64=$(echo -ne "$(echo -n $(sha256sum ${VERSION}/update.gz | awk '{print $1}') | sed -e 's/../\\x&/g')" | base64)

XML="<?xml version=\"1.0\" encoding=\"UTF-8\"?>
<response protocol=\"3.0\" server=\"update.core-os.net\">
 <daystart elapsed_seconds=\"0\"></daystart>
 <app appid=\"e96281a6-d1af-4bde-9a0a-97b76e56dc57\" status=\"ok\">
  <updatecheck status=\"ok\">
   <urls>
    <url codebase=\"${URL}/${VERSION}/\"></url>
   </urls>
   <manifest version=\"${VERSION}\">
    <packages>
     <package hash=\"${SHA1_b64}\" name=\"update.gz\" size=\"${SIZE}\" required=\"false\"></package>
    </packages>
    <actions>
     <action event=\"postinstall\" ChromeOSVersion=\"\" sha256=\"${SHA256_b64}\" needsadmin=\"false\" IsDelta=\"false\" DisablePayloadBackoff=\"true\"></action>
    </actions>
   </manifest>
  </updatecheck>
 </app>
</response>" 

echo "$XML" > $VERSION/index.html
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run script (it will download update image and create metadata file):
./bash.sh 723.3.0

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Run nginx:

docker run -ti --rm --net=host -v ${PWD}:/etc/nginx/conf.d -v ${PWD}:/home/coreos_updates nginx
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directory tree should be like:

find /home/coreos_updates/
/home/coreos_updates/
/home/coreos_updates/amd64-usr
/home/coreos_updates/amd64-usr/723.3.0
/home/coreos_updates/amd64-usr/723.3.0/update.gz
/home/coreos_updates/amd64-usr/723.3.0/index.html

Then run "update_engine_client -update" inside CoreOS.