SERVER-47047 Add tests that mongos does not mark a node as down when reads fail

jstests/sharding/mongos_not_mark_nodes_as_down_when_reads_fail.js

@@ -0,0 +1,69 @@
+/*
+ * Tests that mongos does not mark nodes as down when reads fail.
+ */
+(function() {
+'use strict';
+
+load("jstests/libs/fail_point_util.js");
+
+/*
+ * Configures failCommand to force the given command to fail with the given error code when run
+ * on the given namespace, and returns the resulting fail point.
+ */
+function configureFailCommand(nodeConn, command, ns, error) {
+    return configureFailPoint(
+        nodeConn,
+        "failCommand",
+        {failInternalCommands: true, errorCode: error, failCommands: [command], namespace: ns});
+}
+
+const st = new ShardingTest({shards: 1, rs: {nodes: [{}, {rsConfig: {priority: 0}}]}});
+const kDbName = "foo";
+const kCollName = "bar";
+const kNs = kDbName + "." + kCollName;
+const kErrorCode = ErrorCodes.HostUnreachable;
+const testDB = st.s.getDB(kDbName);
+
+assert.commandWorked(st.s.adminCommand({enableSharding: kDbName}));
+assert.commandWorked(st.s.adminCommand({shardCollection: kNs, key: {x: 1}}));
+
+jsTest.log("Test that mongos does not mark the primary node as down when reads fail");
+(() => {
+    const cmdObj = {
+        count: kCollName,
+        query: {x: {$gte: 0}},
+        $readPreference: {mode: "primary"},
+    };
+
+    // Make the command fail on the primary node with HostUnreachable.
+    const failPoint = configureFailCommand(st.rs0.nodes[0], "count", kNs, kErrorCode);
+    assert.commandFailedWithCode(testDB.runCommand(cmdObj), kErrorCode);
+    failPoint.off();
+
+    // Verify that the node was not marked as down (i.e. it is still the primary node and the
+    // command with readPreference "primary" works).
+    awaitRSClientHosts(st.s, st.rs0.nodes[0], {ok: true, ismaster: true});
+    assert.commandWorked(testDB.runCommand(cmdObj));
+})();
+
+jsTest.log("Test that mongos does not mark the secondary node as down when reads fail");
+(() => {
+    const cmdObj = {
+        count: kCollName,
+        query: {x: {$gte: 0}},
+        $readPreference: {mode: "secondary"},
+    };
+
+    // Make the command fail on the secondary node.
+    const failPoint = configureFailCommand(st.rs0.nodes[1], "count", kNs, kErrorCode);
+    assert.commandFailedWithCode(testDB.runCommand(cmdObj), kErrorCode);
+    failPoint.off();
+
+    // Verify that the node was not marked as down (i.e. it is still the secondary node and the
+    // command with readPreference "secondary" works).
+    awaitRSClientHosts(st.s, st.rs0.nodes[1], {ok: true, secondary: true});
+    assert.commandWorked(testDB.runCommand(cmdObj));
+})();
+
+st.stop();
+})();