JavaAndroid.java

PNConfiguration configPrimary = new PNConfiguration(new UserId("myUserId"));
configPrimary.setSubscribeKey("mySubscribeKey");
configPrimary.setPublishKey("myPublishKey");
configPrimary.setOrigin("primary.pubnubapi.com");

PNConfiguration configBackupOne = new PNConfiguration(new UserId("myUserId"));
configBackupOne.setSubscribeKey("mySubscribeKey");
configBackupOne.setPublishKey("myPublishKey");
configBackupOne.setOrigin("backup-1.pubnubapi.com");

PNConfiguration configBackupTwo = new PNConfiguration(new UserId("myUserId"));
configBackupTwo.setSubscribeKey("mySubscribeKey");
configBackupTwo.setPublishKey("myPublishKey");
configBackupTwo.setOrigin("backup-2.pubnubapi.com");

int currentConfig = 0;
Timer restoreTimer;
PubNub pubnubPrimary = new PubNub(configPrimary);
PubNub pubnubBackupOne = new PubNub(configBackupOne);
PubNub pubnubBackupTwo = new PubNub(configBackupTwo);

SubscribeCallback subscribeCallback = new SubscribeCallback() {
    @Override
    public void status(PubNub pubnub, PNStatus status) {
        switch (status.getOperation()) {
            // combine unsubscribe and subscribe handling for ease of use
            case PNSubscribeOperation:
            case PNUnsubscribeOperation:
                // Note: subscribe statuses never have traditional errors,
                // just categories to represent different issues or successes
                // that occur as part of subscribe
                switch (status.getCategory()) {
                    case PNUnexpectedDisconnectCategory:
                        restorePrimaryTimer();
                        pubnubPrimary.unsubscribeAll();
                        if (currentBackupConfig == 1) {
                            pubnubBackupOne.unsubscribeAll();
                            pubnubBackupTwo.subscribe().channels(Arrays.asList("my_channel")).execute();
                            currentBackupConfig = 2;
                        }
                        else {
                            pubnubBackupTwo.unsubscribeAll();
                            pubnubBackupOne.subscribe().channels(Arrays.asList("my_channel")).execute();
                            currentBackupConfig = 1;
                        }
                }
        }
    }
};

pubnubPrimary.addListener(subscribeCallback);
pubnubBackupOne.addListener(subscribeCallback);
pubnubBackupTwo.addListener(subscribeCallback);

public void restorePrimaryTimer() {
    if (restoreTimer) restoreTimer.cancel();
    restoreTimer = new Timer().scheduleAtFixedRate(new TimerTask(){
        @Override
        public void run(){
            pubnubPrimary.subscribe().channels(Arrays.asList("my_channel")).execute();
            pubnubBackupOne.unsubscribeAll();
            pubnubBackupTwo.unsubscribeAll();
        }
    }, 0, 60 * 1000);
}

JavaScript.html

<script src="https://cdn.pubnub.com/sdk/javascript/pubnub.7.2.1.js"></script>

<script>
let currentConfig = "primary";
let configs = {
    primary : { publishKey : "myPublishKey", subscribeKey : "mySubscribeKey", userId: "myUniqueUserId", origin: "primary.pubnubapi.com" },
    backup1 : { publishKey : "myPublishKey", subscribeKey : "mySubscribeKey", userId: "myUniqueUserId", origin: "backup-1.pubnubapi.com" },
    backup2 : { publishKey : "myPublishKey", subscribeKey : "mySubscribeKey", userId: "myUniqueUserId", origin: "backup-2.pubnubapi.com" },
};

let pubnub = new initPubNubSDK(configs[currentConfig]);

const listener = {
    status: (statusEvent) => {
        if (statusEvent.category === "PNUnexpectedDisconnectCategory") {
            if (currentConfig === "backup1") {
                currentConfig = "backup2";
            }
            else {
                currentConfig = "backup1";
            }

            clearTimeout(pubnub.restorePrimaryTimer);
            pubnub = initPubNubSDK(configs[currentConfig]);
            pubnub.restorePrimaryTimer = setTimeout( () => {
                fetch(`https://${configs["primary"].origin}/time/0`)
                   .then((response) => {
                       currentConfig = "primary";
                       pubnub = initPubNubSDK(configs[currentConfig]);
                   });
            }, 60 * 1000 );
        }
    },
    message: (messageEvent) => {
        // handle messages
    },
    presence: (presenceEvent) => {
        // handle presence
    }
};

function initPubNubSDK(config) { 
    let pubnub = new PubNub(config);
    pubnub.subscribe({ channels: ["hello_world"] });
    pubnub.addListener(listener);
    return pubnub;
}
</script>

JavaServer.java

PNConfiguration configPrimary = new PNConfiguration(new UserId("myUserId"));
configPrimary.setSubscribeKey("mySubscribeKey");
configPrimary.setPublishKey("myPublishKey");
configPrimary.setOrigin("primary.pubnubapi.com");

PNConfiguration configBackupOne = new PNConfiguration(new UserId("myUserId"));
configBackupOne.setSubscribeKey("mySubscribeKey");
configBackupOne.setPublishKey("myPublishKey");
configBackupOne.setOrigin("backup-1.pubnubapi.com");

PNConfiguration configBackupTwo = new PNConfiguration(new UserId("myUserId"));
configBackupTwo.setSubscribeKey("mySubscribeKey");
configBackupTwo.setPublishKey("myPublishKey");
configBackupTwo.setOrigin("backup-2.pubnubapi.com");

PubNub pubnubPrimary = new PubNub(configPrimary);
PubNub pubnubBackupOne = new PubNub(configBackupOne);
PubNub pubnubBackupTwo = new PubNub(configBackupTwo);

pubnubPrimary.publish().channel(channelName).message(messageJsonObject).async((result, publishStatus) -> {
    if (publishStatus.isError()) {
        // Retry next endpoint
        pubnubBackupOne.publish().channel(channelName).message(messageJsonObject).async((result, publishStatus) -> {
            if (publishStatus.isError()) {
                // Retry next endpoint
                pubnubBackupTwo.publish().channel(channelName).message(messageJsonObject).async((result, publishStatus) -> {
                    if (publishStatus.isError()) {
                        // Retry next endpoint
                    }
                });
            }
        });
    }
});

ObjectiveC.m

#import <PubNub/PubNub.h>

PNConfiguration *configPrimary = [PNConfiguration configurationWithPublishKey: @"myPublishKey" subscribeKey:@"mySubscribeKey"];
PNConfiguration *configBackupOne = [PNConfiguration configurationWithPublishKey: @"myPublishKey" subscribeKey:@"mySubscribeKey"];
PNConfiguration *configBackupTwo = [PNConfiguration configurationWithPublishKey: @"myPublishKey" subscribeKey:@"mySubscribeKey"];

configPrimary.origin = @"primary.pubnubapi.com";
configPrimary.uuid = @"myUniqueUUID";

configBackupOne.origin = @"backup-1.pubnubapi.com";
configBackupOne.uuid = @"myUniqueUUID";

configBackupTwo.origin = @"backup-2.pubnubapi.com";
configBackupTwo.uuid = @"myUniqueUUID";

self.client = [PubNub clientWithConfiguration:configPrimary];

[pubnub addListener:self];

- (void)client:(PubNub *)pubnub didReceiveStatus:(PNStatus *)status {
    PNStatusCategory category = status.category; // One of PNStatusCategory fields to identify status of operation processing
    PNOperationType operation = status.operation; // One of PNOperationType fields to identify for which operation status received
    BOOL isError = status.isError; // Whether any kind of error happened.
    NSInteger statusCode = status.statusCode; // Related request processing status code
    BOOL isTLSEnabled = status.isTLSEnabled; // Whether secured connection enabled
    NSString *uuid = status.uuid; // UUID which configured for passed client
    NSString *authKey = status.authKey; // Auth key configured for passed client
    NSString *origin = status.origin; // Origin against which request has been sent
    NSURLRequest *clientRequest = status.clientRequest; // Request which has been used to send last request (may be nil)
    BOOL willAutomaticallyRetry = status.willAutomaticallyRetry; // Whether client will try to perform automatic retry

    if (isError && category == PNUnexpectedDisconnectCategory) {
        // Check if we are on first backup, then use secondary backup
        if (self.client.configuration.origin == backupOne.origin)
            PNConfiguration *backup = backupTwo;
         }
         else {
            PNConfiguration *backup = backupOne; 
         }

        // Re-initialize with backup config
        self.client = [PubNub clientWithConfiguration:backup];

        // Re-subscribe to channels
        [self.client subscribeToChannels: @[@"hello-world-channel"]];

        // Start restore primary timer
        NSTimer *timer = [NSTimer scheduledTimerWithTimeInterval:60 target:self selector:@selector(restorePrimaryConfiguration) userInfo:nil repeats:NO];
    }
}

-(void)restorePrimaryConfiguration
{
    // Test primary origin
    url = [NSString stringWithFormat:@"https://%@/time/0", configPrimary.origin];
    if ([getDataFrom url] == nil) {
        // Start retry timer again
        NSTimer *timer = [NSTimer scheduledTimerWithTimeInterval:60 target:self selector:@selector(restorePrimaryConfiguration) userInfo:nil repeats:NO];
        return;
    }

    // Re-initialize with backup config
    self.client = [PubNub clientWithConfiguration:configPrimary];

    // Re-subscribe to channels
    [self.client subscribeToChannels: @[@"hello-world-channel"]];
}

- (NSString *) getDataFrom:(NSString *)url{
    NSMutableURLRequest *request = [[NSMutableURLRequest alloc] init];
    [request setHTTPMethod:@"GET"];
    [request setURL:[NSURL URLWithString:url]];

    NSError *error = nil;
    NSHTTPURLResponse *responseCode = nil;

    NSData *oResponseData = [NSURLConnection sendSynchronousRequest:request returningResponse:&responseCode error:&error];

    if([responseCode statusCode] != 200){
        NSLog(@"Error getting %@, HTTP status code %i", url, [responseCode statusCode]);
        return nil;
    }

    return [[NSString alloc] initWithData:oResponseData encoding:NSUTF8StringEncoding]; 
}