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Upgrading

Upgrading a live instance is not recommended. Doing so can put your instance into an odd state resulting in service-unavailability the applications making use of your instance.

Upgrading with zero downtime is achievable. We will do that.

Zero-downtime Upgrading

We can achieve zero downtime for applications that use an existing instance by creating a second instance and using that instead. The first instance can then be removed.

Pre-requisites:

Scenario:

  • create instance-y (second instance)
  • configure instance-y and get it running
  • configure relevant applications on the host to use instance-y
  • remove instance-x

Creating the Second Instance (instance-y)

##########
# GET CODE
##########

# Create a directory for the application and get the code
mkdir -p /var/www/async-http-retriever/instance-y
cd /var/www/async-http-retriever/instance-y
git clone git@github.com:webignition/async-http-retriever.git .

# Create a directory for the MySQL data files for this instance
mkdir -p /var/docker-mysql/async-http-retriever-y

# Change to the docker directory as that is where all the fun happens
cd docker

###########
# CONFIGURE
###########

# Create the configuration
cp .env.dist .env

# We need to set the MySQL data path on the host
sed -i 's|MYSQL_DATA_PATH_ON_HOST|/var/docker-mysql/async-http-retriever-y|g' .env

# Set the rabbit-mq management port to not be the same as instance-x
sed -i 's|15672|35672|g' .env

# Set the application port to not be the same as instance-x
sed -i 's|8001|8003|g' .env

#########
# INSTALL
#########

ID=instance-y docker-compose -p instance-y up -d --build
ID=instance-y docker-compose -p instance-y exec -T app-web composer install
ID=instance-y docker-compose -p instance-y exec -T app-web ./bin/console doctrine:migrations:migrate --no-interaction
ID=instance-y docker-compose -p instance-y down
ID=instance-y docker-compose -p instance-y up -d

Configure Applications to Use instance-y

You managed to configure relevant applications to use instance-x. Do the same but for instance-y.

You configure all relevant applications to use instance-y and that, once done, no applications are using instance-x.

Removing the First Instance

# Change to the docker directory as that is where all the fun happens
cd /var/www/async-http-retriever/instance-x/docker

# Stop and remove containers
ID=instance-x docker-compose -p instance-x down

# Remove instance-x
cd /var/www/async-http-retriever
rm -rf cd /var/www/async-http-retriever/instance-x

# Remove MySQL data files
rm -rf /var/docker-mysql/async-http-retriever-x
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