A network namespace is a logical copy of the network stack from the host system. Network namespaces are useful for setting up containers or virtual environments. Each namespace has its own IP addresses, network interfaces, routing tables, and so forth. The default or global namespace is the one in which the host system physical interfaces exist.
Namespace-specific address spaces can lead to problems when MySQL
connections cross namespaces. For example, the network address
space for a MySQL instance running in a container or virtual
network may differ from the address space of the host machine.
This can produce phenomena such as a client connection from an
address in one namespace appearing to the MySQL server to be
coming from a different address, even for client and server
running on the same machine. Suppose that both processes run on a
host with IP address
203.0.113.10 but use
different namespaces. A connection may produce a result like this:
$> mysql --user=admin --host=203.0.113.10 --protocol=tcp mysql> SELECT USER(); +--------------------+ | USER() | +--------------------+ | email@example.com | +--------------------+
In this case, the expected
firstname.lastname@example.org. Such behavior can
make it difficult to assign account permissions properly if the
address from which an connection originates is not what it
To address this issue, MySQL enables specifying the network namespace to use for TCP/IP connections, so that both endpoints of connections use an agreed-upon common address space.
MySQL supports network namespaces on platforms that implement them. Support within MySQL applies to:
The MySQL server, mysqld.
The mysql client and the mysqlxtest test suite client. (Other clients are not supported. They must be invoked from within the network namespace of the server to which they are to connect.)
Group Replication, only when using the MySQL communication stack to establish group communication connections.
The following sections describe how to use network namespaces in MySQL:
Prior to using network namespace support in MySQL, these host system prerequisites must be satisfied:
The host operating system must support network namespaces. (For example, Linux.)
Any network namespace to be used by MySQL must first be created on the host system.
Host name resolution must be configured by the system administrator to support network namespaces.Note
A known limitation is that, within MySQL, host name resolution does not work for names specified in network namespace-specific host files. For example, if the address for a host name in the
rednamespace is specified in the
/etc/netns/red/hostsfile, binding to the name fails on both the server and client sides. The workaround is to use the IP address rather than the host name.
CAP_SYS_ADMINis a security sensitive operation because it enables a process to perform other privileged actions in addition to setting namespaces. For a description of its effects, see https://man7.org/linux/man-pages/man7/capabilities.7.html.
CAP_SYS_ADMINmust be enabled explicitly by the system administrator, MySQL binaries by default do not have network namespace support enabled. The system administrator should evaluate the security implications of running MySQL processes with
CAP_SYS_ADMINbefore enabling it.
The instructions in the following example set up network
blue. The names you choose may differ, as may
the network addresses and interfaces on your host system.
Invoke the commands shown here either as the
root operating system user or by prefixing
each command with sudo. For example, to
invoke the ip or setcap
command if you are not
sudo ip or sudo setcap.
To configure network namespaces, use the ip command. For some operations, the ip command must execute within a particular namespace (which must already exist). In such cases, begin the command like this:
ip netns exec namespace_name
For example, this command executes within the
red namespace to bring up the loopback
ip netns exec red ip link set lo up
To add namespaces named
blue, each with its own virtual Ethernet
device used as a link between namespaces and its own loopback
ip netns add red ip link add veth-red type veth peer name vpeer-red ip link set vpeer-red netns red ip addr add 192.0.2.1/24 dev veth-red ip link set veth-red up ip netns exec red ip addr add 192.0.2.2/24 dev vpeer-red ip netns exec red ip link set vpeer-red up ip netns exec red ip link set lo up ip netns add blue ip link add veth-blue type veth peer name vpeer-blue ip link set vpeer-blue netns blue ip addr add 198.51.100.1/24 dev veth-blue ip link set veth-blue up ip netns exec blue ip addr add 198.51.100.2/24 dev vpeer-blue ip netns exec blue ip link set vpeer-blue up ip netns exec blue ip link set lo up # if you want to enable inter-subnet routing... sysctl net.ipv4.ip_forward=1 ip netns exec red ip route add default via 192.0.2.1 ip netns exec blue ip route add default via 198.51.100.1
A diagram of the links between namespaces looks like this:
red global blue 192.0.2.2 <=> 192.0.2.1 (vpeer-red) (veth-red) 198.51.100.1 <=> 198.51.100.2 (veth-blue) (vpeer-blue)
To check which namespaces and links exist:
ip netns list ip link list
To see the routing tables for the global and named namespaces:
ip route show ip netns exec red ip route show ip netns exec blue ip route show
To remove the
links and namespaces:
ip link del veth-red ip link del veth-blue ip netns del red ip netns del blue sysctl net.ipv4.ip_forward=0
So that the MySQL binaries that include network namespace
support can actually use namespaces, you must grant them the
CAP_SYS_ADMIN capability. The following
setcap commands assume that you have changed
location to the directory containing your MySQL binaries (adjust
the pathname for your system as necessary):
CAP_SYS_ADMIN capability to the
setcap cap_sys_admin+ep ./mysqld setcap cap_sys_admin+ep ./mysql setcap cap_sys_admin+ep ./mysqlxtest
$> getcap ./mysqld ./mysql ./mysqlxtest ./mysqld = cap_sys_admin+ep ./mysql = cap_sys_admin+ep ./mysqlxtest = cap_sys_admin+ep
setcap -r ./mysqld setcap -r ./mysql setcap -r ./mysqlxtest
If you reinstall binaries to which you have previously applied
setcap, you must use
setcap again. For example, if you perform
an in-place MySQL upgrade, failure to grant the
CAP_SYS_ADMIN capability again results in
namespace-related failures. The server fails with this error
for attempts to bind to an address with a named namespace:
[ERROR] [MY-013408] [Server] setns() failed with error 'Operation not permitted'
A client invoked with the
--network-namespace option fails
ERROR: Network namespace error: Operation not permitted
Assuming that the preceding host system prerequisites have been satisfied, MySQL enables configuring the server-side namespace for the listening (inbound) side of connections and the client-side namespace for the outbound side of connections.
On the server side, the
variables have extended syntax for specifying the network
namespace to use for a given IP address or host name on which to
listen for incoming connections. To specify a namespace for an
address, add a slash and the namespace name. For example, a
my.cnf file might contain these
[mysqld] bind_address = 127.0.1.1,192.0.2.2/red,198.51.100.2/blue admin_address = 126.96.36.199/red mysqlx_bind_address = 188.8.131.52/red
These rules apply:
A network namespace can be specified for an IP address or a host name.
A network namespace cannot be specified for a wildcard IP address.
For a given address, the network namespace is optional. If given, it must be specified as a
/suffix immediately following the address.
An address with no
/suffix uses the host system global namespace. The global namespace is therefore the default.
An address with a
/suffix uses the namespace named
The host system must support network namespaces and each named namespace must previously have been set up. Naming a nonexistent namespace produces an error.
If an error occurs during server startup for attempts to use a namespace, the server does not start. If errors occur for X Plugin during plugin initialization such that it is unable to bind to any address, the plugin fails its initialization sequence and the server does not load it.
On the client side, a network namespace can be specified in these contexts:
mysql --host=192.0.2.2 --network-namespace=red
--network-namespaceoption is omitted, the connection uses the default (global) namespace.
For replication connections from replica servers to source servers, use the
CHANGE REPLICATION SOURCE TOstatement and specify the
NETWORK_NAMESPACEoption. For example:
CHANGE REPLICATION SOURCE TO SOURCE_HOST = '192.0.2.2', NETWORK_NAMESPACE = 'red';
NETWORK_NAMESPACEoption is omitted, replication connections use the default (global) namespace.
The following example sets up a MySQL server that listens for
connections in the global,
blue namespaces, and shows how to configure
accounts that connect from the
blue namespaces. It is assumed that the
have already been created as shown in
Host System Prerequisites.
Configure the server to listen on addresses in multiple namespaces. Put these lines in the server
my.cnffile and start the server:
[mysqld] bind_address = 127.0.1.1,192.0.2.2/red,198.51.100.2/blue
The value tells the server to listen on the loopback address
127.0.0.1in the global namespace, the address
rednamespace, and the address
Connect to the server in the global namespace and create accounts that have permission to connect from an address in the address space of each named namespace:
$> mysql -u root -h 127.0.0.1 -p Enter password: root_password mysql> CREATE USER 'red_user'@'192.0.2.2' IDENTIFIED BY 'red_user_password'; mysql> CREATE USER 'blue_user'@'198.51.100.2' IDENTIFIED BY 'blue_user_password';
Verify that you can connect to the server in each named namespace:
$> mysql -u red_user -h 192.0.2.2 --network-namespace=red -p Enter password: red_user_password mysql> SELECT USER(); +--------------------+ | USER() | +--------------------+ | email@example.com | +--------------------+
$> mysql -u blue_user -h 198.51.100.2 --network-namespace=blue -p Enter password: blue_user_password mysql> SELECT USER(); +------------------------+ | USER() | +------------------------+ | firstname.lastname@example.org | +------------------------+Note
You might see different results from
USER(), which can return a value that includes a host name rather than an IP address if your DNS is configured to be able to resolve the address to the corresponding host name and the server is not run with the
skip_name_resolvesystem variable enabled.
For replication monitoring purposes, these information sources have a column that displays the applicable network namespace for connections:
The Performance Schema
replication_connection_configurationtable. See Section 184.108.40.206, “The replication_connection_configuration Table”.
The replica server connection metadata repository. See Section 220.127.116.11, “Replication Metadata Repositories”.
SHOW REPLICA STATUSstatement.