public com.google.protobuf.ByteString getTpuTopologyBytes() {
      java.lang.Object ref = tpuTopology_;
      if (ref instanceof String) {
        com.google.protobuf.ByteString b =
            com.google.protobuf.ByteString.copyFromUtf8((java.lang.String) ref);
        tpuTopology_ = b;
        return b;
      } else {
        return (com.google.protobuf.ByteString) ref;
      }
    }
<pre>
Immutable. The topology of the TPUs. Corresponds to the TPU topologies
available from GKE. (Example: tpu_topology: "2x2x1").
</pre>

<code>string tpu_topology = 4 [(.google.api.field_behavior) = IMMUTABLE];</code>

@return The bytes for tpuTopology.
java-vertexai/proto-google-cloud-vertexai-v1/src/main/java/com/google/cloud/vertexai/api/MachineSpec.java