On Tue, Aug 1, 2017 at 9:19 AM, Russell Bryant <russ...@ovn.org> wrote:
>
> Add native support for active-standby HA in ovn-northd by having each
> instance attempt to acquire an OVSDB lock. Only the instance of
> ovn-northd that currently holds the lock will make active changes to
> the OVN databases.
>
> Signed-off-by: Russell Bryant <russ...@ovn.org>
> ---
> NEWS | 1 +
> ovn/northd/ovn-northd.8.xml | 9 +++++++++
> ovn/northd/ovn-northd.c | 40 +++++++++++++++++++++++++++++++---------
> 3 files changed, 41 insertions(+), 9 deletions(-)
>
> diff --git a/NEWS b/NEWS
> index facea0228..f3cdd2443 100644
> --- a/NEWS
> +++ b/NEWS
> @@ -49,6 +49,7 @@ Post-v2.7.0
> one chassis is specified, OVN will manage high availability for
that
> gateway.
> * Add support for ACL logging.
> + * ovn-northd now has native support for active-standby high
availability.
> - Tracing with ofproto/trace now traces through recirculation.
> - OVSDB:
> * New support for role-based access control (see ovsdb-server(1)).
> diff --git a/ovn/northd/ovn-northd.8.xml b/ovn/northd/ovn-northd.8.xml
> index 1527e8a60..0d85ec0d2 100644
> --- a/ovn/northd/ovn-northd.8.xml
> +++ b/ovn/northd/ovn-northd.8.xml
> @@ -72,6 +72,15 @@
> </dl>
> </p>
>
> + <h1>Active-Standby for High Availability</h1>
> + <p>
> + You may run <code>ovn-northd</code> more than once in an OVN
deployment.
> + OVN will automatically ensure that only one of them is active at a
time.
> + If multiple instances of <code>ovn-northd</code> are running and
the
> + active <code>ovn-northd</code> fails, one of the hot standby
instances
> + of <code>ovn-northd</code> will automatically take over.
> + </p>
> +
> <h1>Logical Flow Table Structure</h1>
>
> <p>
> diff --git a/ovn/northd/ovn-northd.c b/ovn/northd/ovn-northd.c
> index 10e0c7ce0..3d2be4267 100644
> --- a/ovn/northd/ovn-northd.c
> +++ b/ovn/northd/ovn-northd.c
> @@ -6531,6 +6531,12 @@ main(int argc, char *argv[])
> ovsdb_idl_add_column(ovnsb_idl_loop.idl, &sbrec_chassis_col_nb_cfg);
> ovsdb_idl_add_column(ovnsb_idl_loop.idl, &sbrec_chassis_col_name);
>
> + /* Ensure that only a single ovn-northd is active in the deployment
by
> + * acquiring a lock called "ovn_northd" on the southbound database
> + * and then only performing DB transactions if the lock is held. */
> + ovsdb_idl_set_lock(ovnsb_idl_loop.idl, "ovn_northd");
> + bool had_lock = false;
> +
> /* Main loop. */
> exiting = false;
> while (!exiting) {
> @@ -6541,15 +6547,29 @@ main(int argc, char *argv[])
> .ovnsb_txn = ovsdb_idl_loop_run(&ovnsb_idl_loop),
> };
>
> - struct chassis_index chassis_index;
> - chassis_index_init(&chassis_index, ctx.ovnsb_idl);
> + if (!had_lock && ovsdb_idl_has_lock(ovnsb_idl_loop.idl)) {
> + VLOG_INFO("ovn-northd lock acquired. "
> + "This ovn-northd instance is now active.");
> + had_lock = true;
> + } else if (had_lock && !ovsdb_idl_has_lock(ovnsb_idl_loop.idl)) {
> + VLOG_INFO("ovn-northd lock lost. "
> + "This ovn-northd instance is now on standby.");
Should it try lock again, if we want it to be standby? Otherwise, this
instance won't have a chance to be active any more.
> + had_lock = false;
> + }
>
> - ovnnb_db_run(&ctx, &chassis_index, &ovnsb_idl_loop);
> - ovnsb_db_run(&ctx, &ovnsb_idl_loop);
> - if (ctx.ovnsb_txn) {
> - check_and_add_supported_dhcp_opts_to_sb_db(&ctx);
> - check_and_add_supported_dhcpv6_opts_to_sb_db(&ctx);
> - check_and_update_rbac(&ctx);
> + struct chassis_index chassis_index;
> + bool destroy_chassis_index = false;
> + if (ovsdb_idl_has_lock(ovnsb_idl_loop.idl)) {
> + chassis_index_init(&chassis_index, ctx.ovnsb_idl);
> + destroy_chassis_index = true;
> +
> + ovnnb_db_run(&ctx, &chassis_index, &ovnsb_idl_loop);
> + ovnsb_db_run(&ctx, &ovnsb_idl_loop);
> + if (ctx.ovnsb_txn) {
> + check_and_add_supported_dhcp_opts_to_sb_db(&ctx);
> + check_and_add_supported_dhcpv6_opts_to_sb_db(&ctx);
> + check_and_update_rbac(&ctx);
> + }
> }
>
> unixctl_server_run(unixctl);
> @@ -6565,7 +6585,9 @@ main(int argc, char *argv[])
> exiting = true;
> }
>
> - chassis_index_destroy(&chassis_index);
> + if (destroy_chassis_index) {
> + chassis_index_destroy(&chassis_index);
> + }
> }
>
> unixctl_server_destroy(unixctl);
> --
> 2.13.3
>
Acked-by: Han Zhou <zhou...@gmail.com>
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