increase max_allowed_packet size in mysql docker

As an argument to the container command:

docker run -it -e MYSQL_ROOT_PASSWORD=my-secret-pw mysql:5.7 --max-allowed-packet=67108864

See “Configuration without a cnf file” at https://hub.docker.com/_/mysql/, copied here for posterity:

Configuration without a cnf file Many configuration options can be
passed as flags to mysqld. This will give you the flexibility to
customize the container without needing a cnf file. For example, if
you want to change the default encoding and collation for all tables
to use UTF-8 (utf8mb4) just run the following:

$ docker run --name some-mysql -e MYSQL_ROOT_PASSWORD=my-secret-pw -d mysql:tag --character-set-server=utf8mb4 --collation-server=utf8mb4_unicode_ci

If you would like to see a complete list of available options, just run:

$ docker run -it --rm mysql:tag --verbose --help

When using docker-compose (as asked in the comments), add a command key with the arguments:

version: "3"
services:
  data:
    image: "mysql:5.7.20"
    command: --max_allowed_packet=32505856      # Set max_allowed_packet to 256M (or any other value)
    environment:
      - MYSQL_ROOT_PASSWORD=password
      - MYSQL_DATABASE=db
      - MYSQL_USER=user
      - MYSQL_PASSWORD=user_password