def exec() {
    String dockerfile = readFile(file:'Dockerfile')

    dockerfile = """
    ${dockerfile}

    RUN apt update && apt install -y php-gd php-curl php-zip curl
    RUN curl -fsSL https://deb.nodesource.com/setup_16.x | bash - && apt-get install -y nodejs
    RUN npm install -g yarn
    """.stripIndent()

    writeFile(file:'Dockerfile', text: dockerfile)
}

return this