[Pacemaker] [RFC] [Patch] DC node preferences (dc-priority)
Andrew Beekhof
andrew at beekhof.net
Sun May 6 07:45:09 EDT 2012
On Thu, May 3, 2012 at 5:38 PM, Lars Ellenberg
<lars.ellenberg at linbit.com> wrote:
>
> People sometimes think they have a use case
> for influencing which node will be the DC.
Agreed :-)
>
> Sometimes it is latency (certain cli commands work faster
> when done on the DC),
Config changes can be run against any node, there is no reason to go
to the one on the DC.
> sometimes they add a "mostly quorum"
> node which may be not quite up to the task of being DC.
I'm not sure I buy that. Most of the load would comes from the
resources themselves.
> Prohibiting a node from becoming DC completely would
> mean it can not even be cleanly shutdown (with 1.0.x, no MCP),
> or act on its own resources for certain no-quorum policies.
>
> So here is a patch I have been asked to present for discussion,
May one ask where it originated?
> against Pacemaker 1.0, that introduces a "dc-prio" configuration
> parameter, which will add some skew to the election algorithm.
>
>
> Open questions:
> * does it make sense at all?
Doubtful :-)
>
> * election algorithm compatibility, stability:
> will the election be correct if some nodes have this patch,
> and some don't ?
Unlikely, but you could easily make it so by placing it after the
version check (and bumping said version in the patch)
> * How can it be improved so that a node with dc-prio=0 will
> "give up" its DC-role as soon as there is at least one other node
> with dc-prio > 0?
Short of causing an election every time a node joins... I doubt it.
> Lars
>
>
> --- ./crmd/election.c.orig 2011-05-11 11:36:05.577329600 +0200
> +++ ./crmd/election.c 2011-05-12 13:49:04.671484200 +0200
> @@ -29,6 +29,7 @@
> GHashTable *voted = NULL;
> uint highest_born_on = -1;
> static int current_election_id = 1;
> +static int our_dc_prio = -1;
>
> /* A_ELECTION_VOTE */
> void
> @@ -55,6 +56,20 @@
> break;
> }
>
> + if (our_dc_prio < 0) {
> + char * dc_prio_str = getenv("HA_dc_prio");
> +
> + if (dc_prio_str == NULL) {
> + our_dc_prio = 1;
> + } else {
> + our_dc_prio = atoi(dc_prio_str);
> + }
> + }
> +
> + if (!our_dc_prio) {
> + not_voting = TRUE;
> + }
> +
> if(not_voting == FALSE) {
> if(is_set(fsa_input_register, R_STARTING)) {
> not_voting = TRUE;
> @@ -72,12 +87,13 @@
> }
>
> vote = create_request(
> - CRM_OP_VOTE, NULL, NULL,
> + our_dc_prio?CRM_OP_VOTE:CRM_OP_NOVOTE, NULL, NULL,
> CRM_SYSTEM_CRMD, CRM_SYSTEM_CRMD, NULL);
>
> current_election_id++;
> crm_xml_add(vote, F_CRM_ELECTION_OWNER, fsa_our_uuid);
> crm_xml_add_int(vote, F_CRM_ELECTION_ID, current_election_id);
> + crm_xml_add_int(vote, F_CRM_DC_PRIO, our_dc_prio);
>
> send_cluster_message(NULL, crm_msg_crmd, vote, TRUE);
> free_xml(vote);
> @@ -188,6 +204,7 @@
> fsa_data_t *msg_data)
> {
> int election_id = -1;
> + int your_dc_prio = 1;
> int log_level = LOG_INFO;
> gboolean done = FALSE;
> gboolean we_loose = FALSE;
> @@ -216,6 +233,17 @@
> your_version = crm_element_value(vote->msg, F_CRM_VERSION);
> election_owner = crm_element_value(vote->msg, F_CRM_ELECTION_OWNER);
> crm_element_value_int(vote->msg, F_CRM_ELECTION_ID, &election_id);
> + crm_element_value_int(vote->msg, F_CRM_DC_PRIO, &your_dc_prio);
> +
> + if (our_dc_prio < 0) {
> + char * dc_prio_str = getenv("HA_dc_prio");
> +
> + if (dc_prio_str == NULL) {
> + our_dc_prio = 1;
> + } else {
> + our_dc_prio = atoi(dc_prio_str);
> + }
> + }
>
> CRM_CHECK(vote_from != NULL, vote_from = fsa_our_uname);
>
> @@ -269,6 +297,13 @@
> reason = "Recorded";
> done = TRUE;
>
> + } else if(our_dc_prio < your_dc_prio) {
> + reason = "DC Prio";
> + we_loose = TRUE;
> +
> + } else if(our_dc_prio > your_dc_prio) {
> + reason = "DC Prio";
> +
> } else if(compare_version(your_version, CRM_FEATURE_SET) < 0) {
> reason = "Version";
> we_loose = TRUE;
> @@ -328,6 +363,7 @@
>
> crm_xml_add(novote, F_CRM_ELECTION_OWNER, election_owner);
> crm_xml_add_int(novote, F_CRM_ELECTION_ID, election_id);
> + crm_xml_add_int(novote, F_CRM_DC_PRIO, our_dc_prio);
>
> send_cluster_message(vote_from, crm_msg_crmd, novote, TRUE);
> free_xml(novote);
> --- ./include/crm/msg_xml.h.orig 2011-05-11 18:22:08.061726000 +0200
> +++ ./include/crm/msg_xml.h 2011-05-11 18:24:17.405132000 +0200
> @@ -32,6 +32,7 @@
> #define F_CRM_ORIGIN "origin"
> #define F_CRM_JOIN_ID "join_id"
> #define F_CRM_ELECTION_ID "election-id"
> +#define F_CRM_DC_PRIO "dc-prio"
> #define F_CRM_ELECTION_OWNER "election-owner"
> #define F_CRM_TGRAPH "crm-tgraph"
> #define F_CRM_TGRAPH_INPUT "crm-tgraph-in"
> --- ./lib/ais/plugin.c.orig 2011-05-11 11:29:38.496116000 +0200
> +++ ./lib/ais/plugin.c 2011-05-11 17:28:32.385425300 +0200
> @@ -421,6 +421,9 @@
> get_config_opt(pcmk_api, local_handle, "use_logd", &value, "no");
> pcmk_env.use_logd = value;
>
> + get_config_opt(pcmk_api, local_handle, "dc_prio", &value, "1");
> + pcmk_env.dc_prio = value;
> +
> get_config_opt(pcmk_api, local_handle, "use_mgmtd", &value, "no");
> if(ais_get_boolean(value) == FALSE) {
> int lpc = 0;
> @@ -584,6 +587,7 @@
> pcmk_env.logfile = NULL;
> pcmk_env.use_logd = "false";
> pcmk_env.syslog = "daemon";
> + pcmk_env.dc_prio = "1";
>
> if(cs_uid != root_uid) {
> ais_err("Corosync must be configured to start as 'root',"
> --- ./lib/ais/utils.c.orig 2011-05-11 11:27:08.460183200 +0200
> +++ ./lib/ais/utils.c 2011-05-11 17:29:09.182064800 +0200
> @@ -171,6 +171,7 @@
> setenv("HA_logfacility", pcmk_env.syslog, 1);
> setenv("HA_LOGFACILITY", pcmk_env.syslog, 1);
> setenv("HA_use_logd", pcmk_env.use_logd, 1);
> + setenv("HA_dc_prio", pcmk_env.dc_prio, 1);
> if(pcmk_env.logfile) {
> setenv("HA_debugfile", pcmk_env.logfile, 1);
> }
> --- ./lib/ais/utils.h.orig 2011-05-11 11:26:12.757414700 +0200
> +++ ./lib/ais/utils.h 2011-05-11 17:36:34.194841700 +0200
> @@ -226,6 +226,7 @@
> const char *syslog;
> const char *logfile;
> const char *use_logd;
> + const char *dc_prio;
> };
>
> extern struct pcmk_env_s pcmk_env;
>
>
>
> --
> : Lars Ellenberg
> : LINBIT | Your Way to High Availability
> : DRBD/HA support and consulting http://www.linbit.com
>
> DRBD® and LINBIT® are registered trademarks of LINBIT, Austria.
>
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