[ansible@ansible ~]$ ansible-vault encrypt_string --vault-id dev@prompt 'dev123' --name dev_db_password >> vaults.yaml 
New vault password (dev): 
Confirm new vault password (dev): 

[ansible@ansible ~]$ ansible-vault encrypt_string --vault-id prod@prompt 'prod123' --name prod_db_password >> vaults.yaml 
New vault password (prod): 
Confirm new vault password (prod): 

[ansible@ansible ~]$ cat vaults.yaml 
dev_db_password: !vault |
          $ANSIBLE_VAULT;1.2;AES256;dev
          34653336386234303265623664386237393761626465626230373133643762613266636434613965
          3439333961393832346231353037663662336565306430310a613264636639643865376561316139
          65663862386134396237383936356630666664346530376235333834633033643135396236613262
          3566653338383735640a323937623663303539346463346338366266353866366234336631613538
          6565
prod_db_password: !vault |
          $ANSIBLE_VAULT;1.2;AES256;prod
          63623637666532326637316432396432393431333664323262363937386238303134303264353436
          3866336533396262626438616630373863366261366533350a663765316337343863356665363763
          36663835643730303734643032643466323732386561633162323332373861656235346462643130
          6465303633356331370a363564653465653666656366353166663039333430656163373939326538
          6531