Authorization

A common question is how to enforce fine-grained access control in Vitess. This question comes up because Vitess uses connection pooling with fixed MySQL users at the VTTablet level, and implements its own authentication at the VTGate level. As a result, you cannot use the normal MySQL GRANTs system to give certain application-level MySQL users more or less permissions than others.

The MySQL GRANT system is very extensive, and we have not reimplemented all of this functionality in Vitess. What we have done is to enable you to provide authorization via table-level ACLs, with a few basic characteristics:

  • Individual users can be assigned 3 levels of permissions:
    • Read (corresponding to read DML, e.g. SELECT)
    • Write (corresponding to write DML, e.g. INSERT, UPDATE, DELETE)
    • Admin (corresponding to DDL, e.g. ALTER TABLE)
  • Permissions are applied on a specified set of tables, which can be enumerated or specified by regex.

VTTablet parameters for table ACLs

Note that the Vitess authorization via ACLs are applied at the VTTablet level, as opposed to on VTGate, where authentication is enforced. There are a number of VTTablet command line parameters that control the behavior of ACLs. Let’s review these:

  • -enforce-tableacl-config: Set this to true to ensure VTTablet will not start unless there is a valid ACL configuration. This is used to catch misconfigurations resulting in blanket access to authenticated users.
  • -queryserver-config-enable-table-acl-dry-run: Set to true to check the table ACL at runtime, and only emit the TableACLPseudoDenied metric if a request would have been blocked. The request is then allowed to pass, even if the ACL determined it should be blocked. This can be used for testing new or updated ACL policies. Default is false.
  • -queryserver-config-strict-table-acl: Set to true to enforce table ACL checking. This needs to be enabled for your ACLs to have any effect. Any users that are not specified in an ACL policy will be denied. Default is false.
  • -queryserver-config-acl-exempt-acl: Allows you to specify the name of an ACL (see below for format) that is exempt from enforcement. Allows you to separate the rollout and the subsequent enforcement of a specific ACL.
  • -table-acl-config: Path to a file defining the table ACL config.
  • -table-acl-config-reload-interval: How often the table-acl-config should be reloaded. Set this to allow you to update the ACL file on disk, and then have VTTablet automatically reload the file within this period. Default is not to reload the ACL file after VTTablet startup. Note that even if you do not set this parameter, you can always force VTTablet to reload the ACL config file from disk by sending a SIGHUP signal to your VTTablet process.

Format of the table ACL config file

The file specified in the -table-acl-config parameter above is a JSON file with the following example to explain the format:

{
    "table_groups": [
        {
            "name": "aclname",
            "table_names_or_prefixes": [
                "%"
            ],
            "readers": [
                "vtgate-user1"
            ],
            "writers": [
                "vtgate-user2"
            ],
            "admins": [
                "vtgate-user3"
            ]
        },
        { "... more ACLs here if necessary ..." }
    ]
}

Notes:

  • name: This is the name of the ACL (aclname in the example above) and is what needs to be specified in -queryserver-config-acl-exempt-acl, if you need to exempt a specific ACL from enforcement.
  • table_names_or_prefixes: A list of strings and/or regexes that allow a rule to target a specific table or set of tables. Use % as in the example to specify all tables. Note that only the SQL % “regex” wildcard is supported here at the moment.
  • readers: A list of VTGate users, specified by their UserData field in the authentication specification, that are allowed to read the tables targeted by this ACL rule. Typically allows SELECT.
  • writers: A list of VTGate users that are allowed to write to the tables targeted by this ACL rule. Typically allows INSERT, UPDATE and DELETE.
  • admins: A list of VTGate users that are allowed admin privileges on the tables targeted by this ACL rule. Typically allows DDL privileges, e.g. ALTER TABLE. Note that this also includes some commands that might be thought of as DML, which are really DDL, like TRUNCATE)
  • Note that writers privilege does not imply readers privilege, and admins privilege does not imply readers or writers. You need to therefore add your users to each list explicitly if you want them to have that level of access.
  • You cannot use multiple ACL rules to target the same (sub)set of tables. Therefore the tablenames specified by table_names_or_prefixes (or expanded by regexes) need to be non-overlapping between ACL rules. Additionally, you cannot have duplicate tablenames or overlapping regexes in the table_names_or_prefixes list in a single ACL rule.

Example

Let’s assume your Vitess cluster already has two keyspaces setup:

  • keyspace1 with a single table t that should only be accessed by myuser1
  • keyspace2 with a single table t that should only be accessed by myuser2

For the VTTablet configuration for keyspace1:

$ cat > acls_for_keyspace1.json << EOF
{
  "table_groups": [
    {
      "name": "keyspace1acls",
      "table_names_or_prefixes": ["%"],
      "readers": ["myuser1", "vitess"],
      "writers": ["myuser1", "vitess"],
      "admins": ["myuser1", "vitess"]
    }
  ]
}
EOF

$ vttablet -init_keyspace "keyspace1" -table-acl-config=acls_for_keyspace1.json -enforce-tableacl-config -queryserver-config-strict-table-acl ........

Note that the % specifier for table_names_or_prefixes translates to “all tables”.

Do the same thing for keyspace2:

$ cat > acls_for_keyspace2.json << EOF
{
  "table_groups": [
    {
      "name": "keyspace2acls",
      "table_names_or_prefixes": ["%"],
      "readers": ["myuser2", "vitess"],
      "writers": ["myuser2", "vitess"],
      "admins": ["myuser2", "vitess"]
    }
  ]
}
EOF

$ vttablet -init_keyspace "keyspace2" -table-acl-config=acls_for_keyspace2.json -enforce-tableacl-config -queryserver-config-strict-table-acl ........

With this setup, the myuser1 and myuser2 users can only access their respective keyspaces, but the vitess user can access both.

# Attempt to access keyspace1 with myuser2 credentials through vtgate
$ mysql -h 127.0.0.1 -u myuser2 -ppassword2 -D keyspace1 -e "select * from t"
ERROR 1045 (HY000) at line 1: vtgate: http://vtgate-zone1-7fbfd8cc47-tchbz:15001/: target: keyspace1.-80.master, used tablet: zone1-476565201 (zone1-keyspace1-x-80-replica-1.vttablet): vttablet: rpc error: code = PermissionDenied desc = table acl error: "myuser2" [] cannot run PASS_SELECT on table "t" (CallerID: myuser2)
target: keyspace1.80-.master, used tablet: zone1-1289569200 (zone1-keyspace1-80-x-replica-0.vttablet): vttablet: rpc error: code = PermissionDenied desc = table acl error: "myuser2" [] cannot run PASS_SELECT on table "t" (CallerID: myuser2)
$

Whereas myuser1 is able to access its keyspace without error:

$ mysql -h 127.0.0.1 -u myuser1 -ppassword1 -D keyspace1 -e "select * from t"
$