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Abstract​

x/upgrade is an implementation of a Cosmos SDK module that facilitates smoothly upgrading a live Cosmos chain to a new (breaking) software version. It accomplishes this by providing a PreBlocker hook that prevents the blockchain state machine from proceeding once a pre-defined upgrade block height has been reached. The module does not prescribe anything regarding how governance decides to do an upgrade, but just the mechanism for coordinating the upgrade safely. Without software support for upgrades, upgrading a live chain is risky because all of the validators need to pause their state machines at exactly the same point in the process. If this is not done correctly, there can be state inconsistencies which are hard to recover from.

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Concepts​

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Plan​

The x/upgrade module defines a Plan type in which a live upgrade is scheduled to occur. A Plan can be scheduled at a specific block height. A Plan is created once a (frozen) release candidate along with an appropriate upgrade Handler (see below) is agreed upon, where the Name of a Plan corresponds to a specific Handler. Typically, a Plan is created through a governance proposal process, where if voted upon and passed, will be scheduled. The Info of a Plan may contain various metadata about the upgrade, typically application specific upgrade info to be included on-chain such as a git commit that validators could automatically upgrade to. 
type Plan struct {  Name   string  Height int64  Info   string}

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Sidecar Process​

If an operator running the application binary also runs a sidecar process to assist in the automatic download and upgrade of a binary, the Info allows this process to be seamless. This tool is Cosmovisor.

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Handler​

The x/upgrade module facilitates upgrading from major version X to major version Y. To accomplish this, node operators must first upgrade their current binary to a new binary that has a corresponding Handler for the new version Y. It is assumed that this version has fully been tested and approved by the community at large. This Handler defines what state migrations need to occur before the new binary Y can successfully run the chain. Naturally, this Handler is application specific and not defined on a per-module basis. Registering a Handler is done via Keeper#SetUpgradeHandler in the application. 
type UpgradeHandler func(Context, Plan, VersionMap) (VersionMap, error)
During each EndBlock execution, the x/upgrade module checks if there exists a Plan that should execute (is scheduled at that height). If so, the corresponding Handler is executed. If the Plan is expected to execute but no Handler is registered or if the binary was upgraded too early, the node will gracefully panic and exit.

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StoreLoader​

The x/upgrade module also facilitates store migrations as part of the upgrade. The StoreLoader sets the migrations that need to occur before the new binary can successfully run the chain. This StoreLoader is also application specific and not defined on a per-module basis. Registering this StoreLoader is done via app#SetStoreLoader in the application. 
func UpgradeStoreLoader (upgradeHeight int64, storeUpgrades *store.StoreUpgrades) baseapp.StoreLoader
If there’s a planned upgrade and the upgrade height is reached, the old binary writes Plan to the disk before panicking. This information is critical to ensure the StoreUpgrades happens smoothly at correct height and expected upgrade. It eliminiates the chances for the new binary to execute StoreUpgrades multiple times everytime on restart. Also if there are multiple upgrades planned on same height, the Name will ensure these StoreUpgrades takes place only in planned upgrade handler.

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Proposal​

Typically, a Plan is proposed and submitted through governance via a proposal containing a MsgSoftwareUpgrade message. This proposal prescribes to the standard governance process. If the proposal passes, the Plan, which targets a specific Handler, is persisted and scheduled. The upgrade can be delayed or hastened by updating the Plan.Height in a new proposal. proto/cosmos/upgrade/v1beta1/tx.proto 
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See full example on GitHub

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Cancelling Upgrade Proposals​

Upgrade proposals can be cancelled. There exists a gov-enabled MsgCancelUpgrade message type, which can be embedded in a proposal, voted on and, if passed, will remove the scheduled upgrade Plan. Of course this requires that the upgrade was known to be a bad idea well before the upgrade itself, to allow time for a vote. proto/cosmos/upgrade/v1beta1/tx.proto 
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See full example on GitHub If such a possibility is desired, the upgrade height is to be 2 * (VotingPeriod + DepositPeriod) + (SafetyDelta) from the beginning of the upgrade proposal. The SafetyDelta is the time available from the success of an upgrade proposal and the realization it was a bad idea (due to external social consensus). A MsgCancelUpgrade proposal can also be made while the original MsgSoftwareUpgrade proposal is still being voted upon, as long as the VotingPeriod ends after the MsgSoftwareUpgrade proposal.

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State​

The internal state of the x/upgrade module is relatively minimal and simple. The state contains the currently active upgrade Plan (if one exists) by key 0x0 and if a Plan is marked as “done” by key 0x1. The state contains the consensus versions of all app modules in the application. The versions are stored as big endian uint64, and can be accessed with prefix 0x2 appended by the corresponding module name of type string. The state maintains a Protocol Version which can be accessed by key 0x3.
  • Plan: 0x0 -> Plan
  • Done: 0x1 | byte(plan name) -> BigEndian(Block Height)
  • ConsensusVersion: 0x2 | byte(module name) -> BigEndian(Module Consensus Version)
  • ProtocolVersion: 0x3 -> BigEndian(Protocol Version)
The x/upgrade module contains no genesis state.

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Events​

The x/upgrade does not emit any events by itself. Any and all proposal related events are emitted through the x/gov module.

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Client​

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CLI​

A user can query and interact with the upgrade module using the CLI.

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Query​

The query commands allow users to query upgrade state. 
simd query upgrade --help
applied​
The applied command allows users to query the block header for height at which a completed upgrade was applied. 
simd query upgrade applied [upgrade-name] [flags]
If upgrade-name was previously executed on the chain, this returns the header for the block at which it was applied. This helps a client determine which binary was valid over a given range of blocks, as well as more context to understand past migrations. Example: 
simd query upgrade applied "test-upgrade"
Example Output: 
"block_id": {    "hash": "A769136351786B9034A5F196DC53F7E50FCEB53B48FA0786E1BFC45A0BB646B5",    "parts": {      "total": 1,      "hash": "B13CBD23011C7480E6F11BE4594EE316548648E6A666B3575409F8F16EC6939E"    }  },  "block_size": "7213",  "header": {    "version": {      "block": "11"    },    "chain_id": "testnet-2",    "height": "455200",    "time": "2021-04-10T04:37:57.085493838Z",    "last_block_id": {      "hash": "0E8AD9309C2DC411DF98217AF59E044A0E1CCEAE7C0338417A70338DF50F4783",      "parts": {        "total": 1,        "hash": "8FE572A48CD10BC2CBB02653CA04CA247A0F6830FF19DC972F64D339A355E77D"      }    },    "last_commit_hash": "DE890239416A19E6164C2076B837CC1D7F7822FC214F305616725F11D2533140",    "data_hash": "E3B0C44298FC1C149AFBF4C8996FB92427AE41E4649B934CA495991B7852B855",    "validators_hash": "A31047ADE54AE9072EE2A12FF260A8990BA4C39F903EAF5636B50D58DBA72582",    "next_validators_hash": "A31047ADE54AE9072EE2A12FF260A8990BA4C39F903EAF5636B50D58DBA72582",    "consensus_hash": "048091BC7DDC283F77BFBF91D73C44DA58C3DF8A9CBC867405D8B7F3DAADA22F",    "app_hash": "28ECC486AFC332BA6CC976706DBDE87E7D32441375E3F10FD084CD4BAF0DA021",    "last_results_hash": "E3B0C44298FC1C149AFBF4C8996FB92427AE41E4649B934CA495991B7852B855",    "evidence_hash": "E3B0C44298FC1C149AFBF4C8996FB92427AE41E4649B934CA495991B7852B855",    "proposer_address": "2ABC4854B1A1C5AA8403C4EA853A81ACA901CC76"  },  "num_txs": "0"}
module versions​
The module_versions command gets a list of module names and their respective consensus versions. Following the command with a specific module name will return only that module’s information. 
simd query upgrade module_versions [optional module_name] [flags]
Example: 
simd query upgrade module_versions
Example Output: 
module_versions:- name: auth  version: "2"- name: authz  version: "1"- name: bank  version: "2"- name: distribution  version: "2"- name: evidence  version: "1"- name: feegrant  version: "1"- name: genutil  version: "1"- name: gov  version: "2"- name: ibc  version: "2"- name: mint  version: "1"- name: params  version: "1"- name: slashing  version: "2"- name: staking  version: "2"- name: transfer  version: "1"- name: upgrade  version: "1"- name: vesting  version: "1"
Example: 
regen query upgrade module_versions ibc
Example Output: 
module_versions:- name: ibc  version: "2"
plan​
The plan command gets the currently scheduled upgrade plan, if one exists. 
regen query upgrade plan [flags]
Example: 
simd query upgrade plan
Example Output: 
height: "130"info: ""name: test-upgradetime: "0001-01-01T00:00:00Z"upgraded_client_state: null

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Transactions​

The upgrade module supports the following transactions:
  • software-proposal - submits an upgrade proposal:
simd tx upgrade software-upgrade v2 --title="Test Proposal" --summary="testing" --deposit="100000000stake" --upgrade-height 1000000 \--upgrade-info '{ "binaries": { "linux/amd64":"https://example.com/simd.zip?checksum=sha256:aec070645fe53ee3b3763059376134f058cc337247c978add178b6ccdfb0019f" } }' --from cosmos1..
  • cancel-software-upgrade - cancels a previously submitted upgrade proposal:
simd tx upgrade cancel-software-upgrade --title="Test Proposal" --summary="testing" --deposit="100000000stake" --from cosmos1..

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REST​

A user can query the upgrade module using REST endpoints.

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Applied Plan​

AppliedPlan queries a previously applied upgrade plan by its name. 
/cosmos/upgrade/v1beta1/applied_plan/{name}
Example: 
curl -X GET "http://localhost:1317/cosmos/upgrade/v1beta1/applied_plan/v2.0-upgrade" -H "accept: application/json"
Example Output: 
{  "height": "30"}

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Current Plan​

CurrentPlan queries the current upgrade plan. 
/cosmos/upgrade/v1beta1/current_plan
Example: 
curl -X GET "http://localhost:1317/cosmos/upgrade/v1beta1/current_plan" -H "accept: application/json"
Example Output: 
{  "plan": "v2.1-upgrade"}

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Module versions​

ModuleVersions queries the list of module versions from state. 
/cosmos/upgrade/v1beta1/module_versions
Example: 
curl -X GET "http://localhost:1317/cosmos/upgrade/v1beta1/module_versions" -H "accept: application/json"
Example Output: 
{  "module_versions": [    {      "name": "auth",      "version": "2"    },    {      "name": "authz",      "version": "1"    },    {      "name": "bank",      "version": "2"    },    {      "name": "distribution",      "version": "2"    },    {      "name": "evidence",      "version": "1"    },    {      "name": "feegrant",      "version": "1"    },    {      "name": "genutil",      "version": "1"    },    {      "name": "gov",      "version": "2"    },    {      "name": "ibc",      "version": "2"    },    {      "name": "mint",      "version": "1"    },    {      "name": "params",      "version": "1"    },    {      "name": "slashing",      "version": "2"    },    {      "name": "staking",      "version": "2"    },    {      "name": "transfer",      "version": "1"    },    {      "name": "upgrade",      "version": "1"    },    {      "name": "vesting",      "version": "1"    }  ]}

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gRPC​

A user can query the upgrade module using gRPC endpoints.

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Applied Plan​

AppliedPlan queries a previously applied upgrade plan by its name. 
cosmos.upgrade.v1beta1.Query/AppliedPlan
Example: 
grpcurl -plaintext \    -d '{"name":"v2.0-upgrade"}' \    localhost:9090 \    cosmos.upgrade.v1beta1.Query/AppliedPlan
Example Output: 
{  "height": "30"}

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Current Plan​

CurrentPlan queries the current upgrade plan. 
cosmos.upgrade.v1beta1.Query/CurrentPlan
Example: 
grpcurl -plaintext localhost:9090 cosmos.slashing.v1beta1.Query/CurrentPlan
Example Output: 
{  "plan": "v2.1-upgrade"}

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Module versions​

ModuleVersions queries the list of module versions from state. 
cosmos.upgrade.v1beta1.Query/ModuleVersions
Example: 
grpcurl -plaintext localhost:9090 cosmos.slashing.v1beta1.Query/ModuleVersions
Example Output: 
{  "module_versions": [    {      "name": "auth",      "version": "2"    },    {      "name": "authz",      "version": "1"    },    {      "name": "bank",      "version": "2"    },    {      "name": "distribution",      "version": "2"    },    {      "name": "evidence",      "version": "1"    },    {      "name": "feegrant",      "version": "1"    },    {      "name": "genutil",      "version": "1"    },    {      "name": "gov",      "version": "2"    },    {      "name": "ibc",      "version": "2"    },    {      "name": "mint",      "version": "1"    },    {      "name": "params",      "version": "1"    },    {      "name": "slashing",      "version": "2"    },    {      "name": "staking",      "version": "2"    },    {      "name": "transfer",      "version": "1"    },    {      "name": "upgrade",      "version": "1"    },    {      "name": "vesting",      "version": "1"    }  ]}

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Resources​

A list of (external) resources to learn more about the x/upgrade module.