jstests/multiVersion/feature_compatibility_version_lagging_secondary.js


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// Tests that a primary with upgrade featureCompatibilityVersion cannot connect with a secondary
// with a lower binary version.
(function() {
    "use strict";

    load("jstests/libs/feature_compatibility_version.js");
    load("jstests/libs/write_concern_util.js");

    const latest = "latest";
    const downgrade = "last-stable";

    function testProtocolVersion(protocolVersion) {
        jsTestLog("Testing connections between mixed-version mixed-featureCompatibilityVersion " +
                  "nodes in a replica set using protocol version " + protocolVersion);

        // Start a new replica set with two latest version nodes.
        let rst = new ReplSetTest({
            protocolVersion: protocolVersion,
            nodes: [{binVersion: latest}, {binVersion: latest, rsConfig: {priority: 0}}],
            settings: {chainingAllowed: false}
        });
        rst.startSet();
        rst.initiate();

        let primary = rst.getPrimary();
        let latestSecondary = rst.getSecondary();

        // Set the featureCompatibilityVersion to the downgrade version so that a downgrade node can
        // join the set.
        assert.commandWorked(
            primary.getDB("admin").runCommand({setFeatureCompatibilityVersion: lastStableFCV}));

        // Add a downgrade node to the set.
        let downgradeSecondary = rst.add({binVersion: downgrade, rsConfig: {priority: 0}});
        rst.reInitiate();

        // Wait for the downgrade secondary to finish initial sync.
        rst.awaitSecondaryNodes();
        rst.awaitReplication();

        // Stop replication on the downgrade secondary.
        stopServerReplication(downgradeSecondary);

        // Set the featureCompatibilityVersion to the upgrade version. This will not replicate to
        // the downgrade secondary, but the downgrade secondary will no longer be able to
        // communicate with the rest of the set.
        assert.commandWorked(primary.adminCommand({setFeatureCompatibilityVersion: latestFCV}));

        // Shut down the latest version secondary.
        rst.stop(latestSecondary);

        // The primary should step down, since it can no longer see a majority of the replica set.
        rst.waitForState(primary, ReplSetTest.State.SECONDARY);

        restartServerReplication(downgradeSecondary);
        rst.stopSet();
    }

    testProtocolVersion(0);
    testProtocolVersion(1);
})();