Deploying OpenStack with kolla-ansible

[Amer E]

I've been trying to deploy openstack using kolla-ansible method according to this guide

but when running:
kolla-ansible -i all-in-one bootstrap-servers -vvv

I get this error after completing few first Tasks:

[WARNING]: Updating cache and auto-installing missing dependency: python3-apt
fatal: [localhost]: FAILED! => {
    "changed": false,
    "cmd": "apt-get update",
    "invocation": {
        "module_args": {
            "allow_downgrade": false,
            "allow_unauthenticated": false,
            "autoclean": false,
            "autoremove": false,
            "cache_valid_time": 0,
            "deb": null,
            "default_release": null,
            "dpkg_options": "force-confdef,force-confold",
            "fail_on_autoremove": false,
            "force": false,
            "force_apt_get": false,
            "install_recommends": null,
            "lock_timeout": 60,
            "only_upgrade": false,
            "package": null,
            "policy_rc_d": null,
            "purge": false,
            "state": "present",
            "update_cache": true,
            "update_cache_retries": 5,
            "update_cache_retry_max_delay": 12,
            "upgrade": "no"
        }
    },
    "msg": "W: GPG error: https://download.docker.com/linux/ubuntu bionic InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 7EA0A9C3F273FCD8\nE: The repository 'https://download.docker.com/linux/ubuntu bionic InRelease' is not signed.",
    "rc": 100,
    "stderr": "W: GPG error: https://download.docker.com/linux/ubuntu bionic InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 7EA0A9C3F273FCD8\nE: The repository 'https://download.docker.com/linux/ubuntu bionic InRelease' is not signed.\n",
    "stderr_lines": [
        "W: GPG error: https://download.docker.com/linux/ubuntu bionic InRelease: The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 7EA0A9C3F273FCD8",
        "E: The repository 'https://download.docker.com/linux/ubuntu bionic InRelease' is not signed."
    ],
    "stdout": "Hit:1 http://ir.archive.ubuntu.com/ubuntu bionic InRelease\nHit:2 http://ir.archive.ubuntu.com/ubuntu bionic-updates InRelease\nHit:3 http://ir.archive.ubuntu.com/ubuntu bionic-backports InRelease\nHit:4 http://ir.archive.ubuntu.com/ubuntu bionic-security InRelease\nHit:5 http://ppa.launchpad.net/deadsnakes/ppa/ubuntu bionic InRelease\nGet:6 https://download.docker.com/linux/ubuntu bionic InRelease [64.4 kB]\nErr:6 https://download.docker.com/linux/ubuntu bionic InRelease\n  The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 7EA0A9C3F273FCD8\nReading package lists...\n",
    "stdout_lines": [
        "Hit:1 http://ir.archive.ubuntu.com/ubuntu bionic InRelease",
        "Hit:2 http://ir.archive.ubuntu.com/ubuntu bionic-updates InRelease",
        "Hit:3 http://ir.archive.ubuntu.com/ubuntu bionic-backports InRelease",
        "Hit:4 http://ir.archive.ubuntu.com/ubuntu bionic-security InRelease",
        "Hit:5 http://ppa.launchpad.net/deadsnakes/ppa/ubuntu bionic InRelease",
        "Get:6 https://download.docker.com/linux/ubuntu bionic InRelease [64.4 kB]",
        "Err:6 https://download.docker.com/linux/ubuntu bionic InRelease",
        "  The following signatures couldn't be verified because the public key is not available: NO_PUBKEY 7EA0A9C3F273FCD8",
        "Reading package lists..."
    ]
}