{"id":845,"date":"2020-02-20T10:09:56","date_gmt":"2020-02-20T10:09:56","guid":{"rendered":"http:\/\/www.andreagirardi.it\/blog\/?p=845"},"modified":"2021-02-04T11:19:21","modified_gmt":"2021-02-04T11:19:21","slug":"mongo-replica-set-with-docker-compose","status":"publish","type":"post","link":"https:\/\/www.andreagirardi.it\/blog\/mongo-replica-set-with-docker-compose\/","title":{"rendered":"Mongo Replica set with docker-compose"},"content":{"rendered":"\n

A replica set<\/em> in MongoDB is a group of mongod<\/a><\/code> processes that maintain the same data set. Replica sets provide redundancy and high availability<\/a> and are the basis for all production deployments. Replication provides redundancy and increases data availability<\/a>. With multiple copies of data on different database servers, replication provides a level of fault tolerance against the loss of a single database server. A replica set contains several data bearing nodes and optionally one arbiter node. Of the data-bearing nodes, one and only one member is deemed the primary node, while the other nodes are deemed secondary nodes. <\/p>\n\n\n\n

The primary node<\/a> receives all write operations. A replica set can have only one primary capable of confirming writes with { w: \"majority\" }<\/code><\/a> write concern. By default, clients read from the primary [1]<\/a>; however, clients can specify a read preference<\/a> to send read operations to secondaries.<\/p>\n\n\n\n

Doing it with docker-compose is pretty simple. The first step is to create the docker-compose.yml<\/em> configuration file:<\/p>\n\n\n\n

version: \"3\"\nservices:\n  mongo1:\n    hostname: mongo1\n    container_name: localmongo1\n    image: mongo:latest\n    volumes:\n      - mongodb1-data:\/data\/db\n      - mongodb1-config:\/data\/configdb\n    expose:\n    - 27017\n    ports:\n      - 27011:27017\n    restart: always\n    entrypoint: [ \"\/usr\/bin\/mongod\", \"--bind_ip_all\", \"--replSet\", \"rs0\" ]\n  mongo2:\n    hostname: mongo2\n    container_name: localmongo2\n    image: mongo:latest\n    volumes:\n      - mongodb2-data:\/data\/db\n      - mongodb2-config:\/data\/configdb\n    expose:\n    - 27017\n    ports:\n    - 27012:27017\n    restart: always\n    entrypoint: [ \"\/usr\/bin\/mongod\", \"--bind_ip_all\", \"--replSet\", \"rs0\" ]\n  mongo3:\n    hostname: mongo3\n    container_name: localmongo3\n    image: mongo:latest\n    volumes:\n      - mongodb3-data:\/data\/db\n      - mongodb3-config:\/data\/configdb\n    expose:\n    - 27017\n    ports:\n    - 27013:27017\n    restart: always\n    entrypoint: [ \"\/usr\/bin\/mongod\", \"--bind_ip_all\", \"--replSet\", \"rs0\" ]\n\nvolumes:\n  mongodb1-data: {}\n  mongodb1-config: {}\n  mongodb2-data: {}\n  mongodb2-config: {}\n  mongodb3-data: {}\n  mongodb3-config: {}\n  proftpd-home: {}<\/code><\/pre>\n\n\n\n
At this point, docker must be started:<\/p>\n\n\n\n
$ docker-compose up \n# or\n$ docker-compose up -d<\/code><\/pre>\n\n\n\n
At this point, enter in one mongo bash and access to mongo console:<\/p>\n\n\n\n
$ docker exec -it localmongo1 \/bin\/bash\n$ mongo<\/code><\/pre>\n\n\n\n
 The last step is to run the DB replica set initialization:<\/p>\n\n\n\n
rs.initiate(\n  {\n    _id : 'rs0',\n    members: [\n      { _id : 0, host : \"mongo1:27017\" },\n      { _id : 1, host : \"mongo2:27017\" },\n      { _id : 2, host : \"mongo3:27017\" }\n    ]\n  }\n)<\/code><\/pre>\n\n\n\n
Now, mongo is ready to accept a connection on port 27011 and, as soon as a  DB \/ collection \/ document is created or updated, it will be replicated on secondary servers.<\/p>\n
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