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https://github.com/outbackdingo/patroni.git
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4872ac51e0
Citus cluster (coordinator and workers) will be stored in DCS as a fleet of Patroni logically grouped together: ``` /service/batman/ /service/batman/0/ /service/batman/0/initialize /service/batman/0/leader /service/batman/0/members/ /service/batman/0/members/m1 /service/batman/0/members/m2 /service/batman/ /service/batman/1/ /service/batman/1/initialize /service/batman/1/leader /service/batman/1/members/ /service/batman/1/members/m1 /service/batman/1/members/m2 ... ``` Where 0 is a Citus group for coordinator and 1, 2, etc are worker groups. Such hierarchy allows reading the entire Citus cluster with a single call to DCS (except Zookeeper). The get_cluster() method will be reading the entire Citus cluster on the coordinator because it needs to discover workers. For the worker cluster it will be reading the subtree of its own group. Besides that we introduce a new method get_citus_coordinator(). It will be used only by worker clusters. Since there is no hierarchical structures on K8s we will use the citus group suffix on all objects that Patroni creates. E.g. ``` batman-0-leader # the leader config map for the coordinator batman-0-config # the config map holding initialize, config, and history "keys" ... batman-1-leader # the leader config map for worker group 1 batman-1-config ... ``` Citus integration is enabled from patroni.yaml: ```yaml citus: database: citus group: 0 # 0 is for coordinator, 1, 2, etc are for workers ``` If enabled, Patroni will create the database, citus extension in it, and INSERTs INTO `pg_dist_authinfo` information required for Citus nodes to communicate between each other, i.e. 'password', 'sslcert', 'sslkey' for superuser if they are defined in the Patroni configuration file. When the new Citus coordinator/worker is bootstrapped, Patroni adds `synchronous_mode: on` to the `bootstrap.dcs` section. Besides that, Patroni takes over management of some Postgres GUCs: - `shared_preload_libraries` - Patroni ensures that the "citus" is added to the first place - `max_prepared_transactions` - if not set or set to 0, Patroni changes the value to `max_connections*2` - wal_level - automatically set to logical. It is used by Citus to move/split shards. Under the hood Citus is creating/removing replication slots and they are automatically added by Patroni to the `ignore_slots` configuration to avoid accidental removal. The coordinator primary actively discovers worker primary nodes and registers/updates them in the `pg_dist_node` table using citus_add_node() and citus_update_node() functions. Patroni running on the coordinator provides the new REST API endpoint: `POST /citus`. It is used by workers to facilitate controlled switchovers and restarts of worker primaries. When the worker primary needs to shut down Postgres because of restart or switchover, it calls the `POST /citus` endpoint on the coordinator and the Patroni on the coordinator starts a transaction and calls `citus_update_node(nodeid, 'host-demoted', port)` in order to pause client connections that work with the given worker. Once the new leader is elected or postgres started back, they perform another call to the `POST/citus` endpoint, that does another `citus_update_node()` call with actual hostname and port and commits a transaction. After transaction is committed, coordinator reestablishes connections to the worker node and client connections are unblocked. If clients don't run long transaction the operation finishes without client visible errors, but only a short latency spike. All operations on the `pg_dist_node` are serialized by Patroni on the coordinator. It allows to have more control and ROLLBACK transaction in progress if its lifetime exceeding a certain threshold and there are other worker nodes should be updated.
85 lines
2.5 KiB
YAML
85 lines
2.5 KiB
YAML
# docker compose file for running a 3-node PostgreSQL cluster
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# with 3-node etcd cluster as the DCS and one haproxy node
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#
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# requires a patroni image build from the Dockerfile:
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# $ docker build -t patroni .
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# The cluster could be started as:
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# $ docker-compose up -d
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# You can read more about it in the:
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# https://github.com/zalando/patroni/blob/master/docker/README.md
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version: "2"
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networks:
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demo:
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services:
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etcd1: &etcd
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image: patroni
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networks: [ demo ]
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environment:
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ETCD_LISTEN_PEER_URLS: http://0.0.0.0:2380
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ETCD_LISTEN_CLIENT_URLS: http://0.0.0.0:2379
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ETCD_INITIAL_CLUSTER: etcd1=http://etcd1:2380,etcd2=http://etcd2:2380,etcd3=http://etcd3:2380
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ETCD_INITIAL_CLUSTER_STATE: new
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ETCD_INITIAL_CLUSTER_TOKEN: tutorial
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container_name: demo-etcd1
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hostname: etcd1
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command: etcd -name etcd1 -initial-advertise-peer-urls http://etcd1:2380
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etcd2:
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<<: *etcd
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container_name: demo-etcd2
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hostname: etcd2
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command: etcd -name etcd2 -initial-advertise-peer-urls http://etcd2:2380
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etcd3:
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<<: *etcd
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container_name: demo-etcd3
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hostname: etcd3
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command: etcd -name etcd3 -initial-advertise-peer-urls http://etcd3:2380
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haproxy:
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image: patroni
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networks: [ demo ]
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env_file: docker/patroni.env
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hostname: haproxy
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container_name: demo-haproxy
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ports:
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- "5000:5000"
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- "5001:5001"
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command: haproxy
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environment: &haproxy_env
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ETCDCTL_ENDPOINTS: http://etcd1:2379,http://etcd2:2379,http://etcd3:2379
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PATRONI_ETCD3_HOSTS: "'etcd1:2379','etcd2:2379','etcd3:2379'"
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PATRONI_SCOPE: demo
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patroni1:
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image: patroni
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networks: [ demo ]
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env_file: docker/patroni.env
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hostname: patroni1
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container_name: demo-patroni1
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environment:
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<<: *haproxy_env
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PATRONI_NAME: patroni1
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patroni2:
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image: patroni
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networks: [ demo ]
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env_file: docker/patroni.env
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hostname: patroni2
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container_name: demo-patroni2
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environment:
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<<: *haproxy_env
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PATRONI_NAME: patroni2
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patroni3:
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image: patroni
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networks: [ demo ]
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env_file: docker/patroni.env
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hostname: patroni3
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container_name: demo-patroni3
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environment:
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<<: *haproxy_env
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PATRONI_NAME: patroni3
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