duplicate key given in txn request while trying to remove all keys by prefix and put them again

Question

Trying to use coreos/jetcd for updating haproxy settings in etcd from Java-code.

What I want to achieve is:

1. remove all endpoints for single host
2. add an updated data for given host

I want to remove all keys by prefix and put actual data in etcd as atomic operation.

That's why I tried to use etcd transactions. My code is:

Op.DeleteOp deleteOp = Op.delete(
        fromString(prefix),
        DeleteOption.newBuilder().withPrefix(fromString(prefix)).build()
);
Txn tx = kvClient.txn().Else(deleteOp);
newKvs.forEach((k,v) -> {
    tx.Else(Op.put(fromString(k), fromString(v), DEFAULT));
});
try {
    tx.commit().get();
} catch (InterruptedException | ExecutionException e) {
    log.error("ETCD transaction failed", e);
    throw new RuntimeException(e);
}

ETCD v3 API is used (etcd v3.2.9). KVstore is initially empty and I want to add 3 records. prefix value is:

/proxy-service/hosts/example.com

and kvs is a Map:

"/proxy-service/hosts/example.com/FTP/0" -> "localhost:10021"
"/proxy-service/hosts/example.com/HTTPS/0" -> "localhost:10443"
"/proxy-service/hosts/example.com/HTTP/0" -> "localhost:10080"

An Exception happens on commit().get() line with the following root cause:

Caused by: io.grpc.StatusRuntimeException: INVALID_ARGUMENT: etcdserver: duplicate key given in txn request
    at io.grpc.Status.asRuntimeException(Status.java:526)
    at io.grpc.stub.ClientCalls$UnaryStreamToFuture.onClose(ClientCalls.java:427)
    at io.grpc.ForwardingClientCallListener.onClose(ForwardingClientCallListener.java:41)
    at com.coreos.jetcd.internal.impl.ClientConnectionManager$AuthTokenInterceptor$1$1.onClose(ClientConnectionManager.java:267)
    at io.grpc.internal.ClientCallImpl.closeObserver(ClientCallImpl.java:419)
    at io.grpc.internal.ClientCallImpl.access$100(ClientCallImpl.java:60)
    at io.grpc.internal.ClientCallImpl$ClientStreamListenerImpl.close(ClientCallImpl.java:493)
    at io.grpc.internal.ClientCallImpl$ClientStreamListenerImpl.access$500(ClientCallImpl.java:422)
    at io.grpc.internal.ClientCallImpl$ClientStreamListenerImpl$1StreamClosed.runInContext(ClientCallImpl.java:525)
    at io.grpc.internal.ContextRunnable.run(ContextRunnable.java:37)
    at io.grpc.internal.SerializingExecutor.run(SerializingExecutor.java:102)
    ... 3 more

What am i doing wrong and how else can I complete several etcd changes as atomic operation?

Instigate

Answer 1

It looks like that the operations to remove a key and then adding a new value for the same key cannot be in the same txn. According to the The etcd APIv3 documentation:

Txn processes multiple requests in a single transaction. A txn request increments the revision of the key-value store and generates events with the same revision for every completed request. It is not allowed to modify the same key several times within one txn.

Niki

Hope this answer is helpful. If you provide more details on why you want the operations to be atomic, I may be able to provide a more detailed solution. – Niki

Well, somehow. Aside from the fact that I should have been able to read ;) I have to phrase a more detailed question. – Anatase