Docker: How to solve the public key error in ubuntu while installing docker

I am getting the below error message when running the below command for installing docker and kubernetes in Ubuntu server. root@master:/home/ubuntu# add-apt-repository \ > "deb [arch=amd64] https://download.docker.com/linux/ubuntu \ > $(lsb_release -cs) \ > stable" Hit:1 http://in.archive.ubuntu.com/ubuntu bionic InRelease Get:2 https://download.docker.com/linux/ubuntu bionic InRelease [64.4 kB] Hit:3 http://in.archive.ubuntu.com/ubuntu bionic-updates InRelease Hit:4 http://in.archive.ubuntu.com/ubuntu bionic-backports InRelease Hit:5 http://in.archive.ubuntu.com/ubuntu bionic-security InRelease **Err:2 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... Done 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.** N: Updating from such a repository can't be done securely, and is therefore disabled by default. N: See apt-secure(8) manpage for repository creation and user configuration details. root@master:/home/ubuntu# I have also ran the below command but no luck root@master:/# sudo apt-key adv --keyserver keyserver.ubuntu.com --recv-keys 7EA0A9C3F273FCD8 Executing: /tmp/apt-key-gpghome.rDOuMCVLF2/gpg.1.sh --keyserver keyserver.ubuntu.com --recv-keys 7EA0A9C3F273FCD8 gpg: keyserver receive failed: No keyserver available