x/circuit

Concepts

Circuit Breaker is a module that is meant to avoid a chain needing to halt/shut down in the presence of a vulnerability, instead the module will allow specific messages or all messages to be disabled. When operating a chain, if it is app specific then a halt of the chain is less detrimental, but if there are applications built on top of the chain then halting is expensive due to the disturbance to applications.

How it works

Circuit Breaker works with the idea that an address or set of addresses have the right to block messages from being executed and/or included in the mempool. Any address with a permission is able to reset the circuit breaker for the message.

The transactions are checked and can be rejected at two points:

• In CircuitBreakerDecorator ante handler:

https://github.com/cosmos/cosmos-sdk/blob/x/circuit/v0.1.0/x/circuit/ante/circuit.go#L27-L41

• With a message router check:

https://github.com/cosmos/cosmos-sdk/blob/release/v0.52.x/baseapp/msg_service_router.go#L123-L133

note

The CircuitBreakerDecorator works for most use cases, but does not check the inner messages of a transaction. This some transactions (such as x/authz transactions or some x/gov transactions) may pass the ante handler. This does not affect the circuit breaker as the message router check will still fail the transaction. This tradeoff is to avoid introducing more dependencies in the x/circuit module. Chains can re-define the CircuitBreakerDecorator to check for inner messages if they wish to do so.

State

Accounts

• AccountPermissions 0x1 | account_address -> ProtocolBuffer(CircuitBreakerPermissions)

type level int32

const (
    // LEVEL_NONE_UNSPECIFIED indicates that the account will have no circuit
    // breaker permissions.
    LEVEL_NONE_UNSPECIFIED = iota
    // LEVEL_SOME_MSGS indicates that the account will have permission to
    // trip or reset the circuit breaker for some Msg type URLs. If this level
    // is chosen, a non-empty list of Msg type URLs must be provided in
    // limit_type_urls.
    LEVEL_SOME_MSGS
    // LEVEL_ALL_MSGS indicates that the account can trip or reset the circuit
    // breaker for Msg's of all type URLs.
    LEVEL_ALL_MSGS 
    // LEVEL_SUPER_ADMIN indicates that the account can take all circuit breaker
    // actions and can grant permissions to other accounts.
    LEVEL_SUPER_ADMIN
)

type Access struct {
    level int32 
    msgs []string // if full permission, msgs can be empty
}

Disable List

List of type urls that are disabled.

• DisableList 0x2 | msg_type_url -> []byte{}

State Transitions

Authorize

Authorize, is called by the module authority (default governance module account) or any account with LEVEL_SUPER_ADMIN to give permission to disable/enable messages to another account. There are three levels of permissions that can be granted. LEVEL_SOME_MSGS limits the number of messages that can be disabled. LEVEL_ALL_MSGS permits all messages to be disabled. LEVEL_SUPER_ADMIN allows an account to take all circuit breaker actions including authorizing and deauthorizing other accounts.

  // AuthorizeCircuitBreaker allows a super-admin to grant (or revoke) another
  // account's circuit breaker permissions.
  rpc AuthorizeCircuitBreaker(MsgAuthorizeCircuitBreaker) returns (MsgAuthorizeCircuitBreakerResponse);

Trip

Trip, is called by an authorized account to disable message execution for a specific msgURL. If empty, all the msgs will be disabled.

  // TripCircuitBreaker pauses processing of Msg's in the state machine.
  rpc TripCircuitBreaker(MsgTripCircuitBreaker) returns (MsgTripCircuitBreakerResponse);

Reset

Reset is called by an authorized account to enable execution for a specific msgURL of previously disabled message. If empty, all the disabled messages will be enabled.

  // ResetCircuitBreaker resumes processing of Msg's in the state machine that
  // have been paused using TripCircuitBreaker.
  rpc ResetCircuitBreaker(MsgResetCircuitBreaker) returns (MsgResetCircuitBreakerResponse);

Messages

MsgAuthorizeCircuitBreaker

https://github.com/cosmos/cosmos-sdk/blob/release/v0.52.x/x/circuit/proto/cosmos/circuit/v1/tx.proto#L25-L40

This message is expected to fail if:

• the granter is not an account with permission level LEVEL_SUPER_ADMIN or the module authority

MsgTripCircuitBreaker

https://github.com/cosmos/cosmos-sdk/blob/release/v0.52.x/x/circuit/proto/cosmos/circuit/v1/tx.proto#L47-L60

This message is expected to fail if:

• if the signer does not have a permission level with the ability to disable the specified type url message

MsgResetCircuitBreaker

https://github.com/cosmos/cosmos-sdk/blob/release/v0.52.x/x/circuit/proto/cosmos/circuit/v1/tx.proto#L67-L78

This message is expected to fail if:

• if the type url is not disabled

Events

The circuit module emits the following events:

Message Events

MsgAuthorizeCircuitBreaker

Type	Attribute Key	Attribute Value
string	granter	{granterAddress}
string	grantee	{granteeAddress}
string	permission	{granteePermissions}
message	module	circuit
message	action	authorize_circuit_breaker

MsgTripCircuitBreaker

Type	Attribute Key	Attribute Value
string	authority	{authorityAddress}
[]string	msg_urls	[]string{msg_urls}
message	module	circuit
message	action	trip_circuit_breaker

ResetCircuitBreaker

Type	Attribute Key	Attribute Value
string	authority	{authorityAddress}
[]string	msg_urls	[]string{msg_urls}
message	module	circuit
message	action	reset_circuit_breaker

Keys

• AccountPermissionPrefix - 0x01
• DisableListPrefix - 0x02

Client

CLI

x/circuit module client provides the following CLI commands:

$ <appd> tx circuit
Transactions commands for the circuit module

Usage:
  simd tx circuit [flags]
  simd tx circuit [command]

Available Commands:
  authorize   Authorize an account to trip the circuit breaker.
  disable     Disable a message from being executed
  reset       Enable a message to be executed

$ <appd> query circuit
Querying commands for the circuit module

Usage:
  simd query circuit [flags]
  simd query circuit [command]

Available Commands:
  account       Query a specific account's permissions
  accounts      Query all account permissions
  disabled-list Query a list of all disabled message types