Storing network state at a network controller

1. For a first network controller located at a first physical domain that manages a logical network spanning a plurality of physical domains including the first physical domain, a method comprising:

storing state information for the logical network in at least two storages;

determining that communication is no longer available with a second network controller at a second of the physical domains spanned by the logical network;

in response to the determination, modifying a first one of the storages to be read-only while leaving a second one of the storages as writeable while communication with the second network controller is not available;

while communication with the second network controller is not available:

receiving input to modify the network state information in the second storage;

modifying the network state information in the second storage based on the input; and

storing the modification to the network state in a local queue of network state updates;

determining that communication with the second network controller has been restored; and

based on the determination that communication has been restored, transmitting the network state updates stored in the local queue to the second network controller.

2. The method of claim 1 further comprising:

while communication with the second network controller is not available:

receiving input to modify the network state information in the first storage; and

returning an error message indicating that the network state information cannot be modified.

3. The method of claim 1 , wherein the first network controller also stores network state information for a plurality of additional logical networks in the first and second storages.

4. The method of claim 1 , wherein the first network controller manages a first set of forwarding elements at the first physical domain and the second network controller manages a second set of forwarding elements at the second physical domain.

5. The method of claim 4 , wherein the forwarding elements at the first and second physical domains implement the logical network as well as a plurality of additional logical networks.

6. The method of claim 1 , wherein the first storage stores network state information that is local to the particular physical domain.

7. The method of claim 1 , wherein the second storage stores global network state information for the logical network that cannot be reconciled between physical domains after a period of disconnection.

8. For a first network controller located at a first domain that manages a logical network spanning a plurality of physical domains including the first domain, a method comprising:

storing state information for the logical network in at least two storages;

determining that communication is no longer available with a second network controller at a second of the physical domains spanned by the logical network;

in response to the determination, modifying a first one of the storages to be read-only while leaving a second one of the storages as writeable while communication with the second network controller is not available; and

while communication with the second network controller is not available:

receiving input to modify the network state information in the second storage;

modifying the network state information in the second storage based on the input;

storing the modification to the network state in a local queue of network state updates;

receiving a second input to modify the network state information in the second storage;

determining that the local queue is full; and

returning an error message indicating that the network state information cannot be modified.

9. The method of claim 8 further comprising:

determining that communication with the second network controller has been restored; and

transmitting the network state updates stored in the local queue to the second network controller.

10. The method of claim 8 , wherein the first network controller manages a first set of forwarding elements at the first physical domain and the second network controller manages a second set of forwarding elements at the second physical domain.

11. The method of claim 10 , wherein the forwarding elements at the first and second physical domains implement the logical network as well as a plurality of additional logical networks.

12. The method of claim 8 , wherein the first network controller also stores network state information for a plurality of additional logical networks in the first and second storages.

13. The method of claim 8 , wherein the first storage stores network state information that is local to the particular physical domain.

14. The method of claim 8 , wherein the second storage stores global network state information for the logical network that cannot be reconciled between physical domains after a period of disconnection.

15. A non-transitory machine readable medium storing a program for a first network controller located at a first domain that manages a logical network spanning a plurality of physical domains including the first domain, the program for execution by at least one processing unit, the program comprising sets of instructions for:

storing a first type of state information for the logical network in a first storage and a second type of state information for the logical network in a second storage;

determining that communication is no longer available with a second network controller at a second of the physical domains spanned by the logical network; and

in response to the determination, modifying the first storage so that the first type of state information is read-only while leaving the second storage as writeable so that the second type of state information is modifiable, while communication with the second network controller is not available;

while communication with the second network controller is not available:

receiving input to modify the network state information in the second storage;

modifying the network state information in the second storage based on the input; and

storing the modification to the network state in a local queue of network state updates;

determining that communication with the second network controller has been restored; and

based on the determination that communication has been restored, transmitting the network state updates stored in the local queue to the second network controller.

16. The non-transitory machine readable medium of claim 15 , wherein the program further comprises sets of instructions for:

while communication with the second network controller is not available:

receiving input to modify the network state information in the first storage; and

returning an error message indicating that the network state information cannot be modified.

17. The non-transitory machine readable medium of claim 15 , wherein the first network controller manages a first set of forwarding elements at the first physical domain and the second network controller manages a second set of forwarding elements at the second physical domain.

18. The non-transitory machine readable medium of claim 17 , wherein the forwarding elements at the first and second physical domains implement the logical network as well as a plurality of additional logical networks.

19. The non-transitory machine readable medium of claim 15 , wherein the first network controller also stores network state information for a plurality of additional logical networks in the first and second storages.

20. The non-transitory machine readable medium of claim 15 , wherein the first storage stores network state information that is local to the particular physical domain.

21. The non-transitory machine readable medium of claim 15 , wherein the second storage stores global network state information for the logical network that cannot be reconciled between physical domains after a period of disconnection.