Shulou(Shulou.com)06/01 Report--

Hidden members of a replication set are configured as priority: 0, and to prevent them from being elected, set hidden: true to prevent clients from connecting to the replication set to route read operations to it, even if they specify a read preference of secondary.

Read from a hidden member, you will see a separate connection instead of a MongoReplicaSetClient type, and specify slave_ok.

Hide member settings

You can use mongo shell to hide a member of a replication set:

Mongo admin-uxucy-p PRIMARY > conf = rs.config () {"_ id": "test", "version": 21, "members": [{"_ id": 0, "host": "xucy.local:27017",}, {"_ id": 1, "host": "xucy.local:28017",}, {"_ id": 2, "host": "xucy.local:29017" }]} PRIMARY > conf.members [1] .priority = 0 PRIMARY > conf.members [1] .hidden = true PRIMARY > conf.version + = 1 PRIMARY > rs.reconfig (conf)

Xucy.local:28017 is now hidden. He will continue to copy and vote in the election as usual, but clients connected to the replication set will not read from it, even if xucy.local:29017 is offline:

Irb (main): 012irb 0 > rs = Mongo::MongoReplicaSetClient.new (["xucy.local:27017", "xucy.local:28017", "xucy.local:29017"]) = > irb (main): 013xucy.local:27017 0 > rs.primary = > ["xucy.local", 27017] irb (main): 014 irb 0 > rs.secondaries = > # # an empty set-as far as this connection is concerned, there are no secondaries.

The report code will look like this (using Ruby):

Require 'mongo' reporting = Mongo::MongoClient.new ("xucy.local", "28017", slave_ok: true) # error checking goes here reporting [' my_application'] ['users'].

Consider

Using hidden members is the easiest way to configure instances for dedicated workloads like reports, however:

Hidden members cannot read in an emergency

With 2 normal and 1 hidden members in a replication set, error tolerance for writes is equivalent to a regular set of 3 members. However, if you lose two nodes, your production application will not be gracefully downgraded to read-only mode because your hidden members will not allow replication set clients to read. If you just like the simplicity of a hidden member, and cost is not a problem, use a collection of 5 members (with a hidden member) instead.

Wrapper code for replication sets cannot be used

Many teams create application-customized wrapper code to add basic knowledge to the client, which is provided by the MongoDB driver. Because you need to use a separate connection to your report instance, you can't reuse the investment, which will make you sad.

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