Transforms

Concepts

Sink

Sink transforms send data out of Shotover to some other service. This is the opposite of Shotover's sources, although sources are not transforms.

Terminating

Every transform chain must have exactly one terminating transform and it must be the final transform of the chain. This means that terminating transforms cannot pass messages onto another transform in the same chain. However some terminating transforms define their own sub-chains to allow further processing of messages.

Debug

Debug transforms can be temporarily used to test how your Shotover configuration performs. Dont forget to remove them when you are finished.

Implementation Status

  • Alpha - Should not be used in production.
  • Beta - Ready for use but is not battle tested.
  • Ready - Ready for use.

Future transforms won't be added to the public API while in alpha. But in these early days we have chosen to publish these alpha transforms to demonstrate the direction we want to take the project.

Transforms

TransformTerminatingImplementation Status
CassandraSinkClusterBeta
CassandraSinkSingleAlpha
CassandraPeersRewriteAlpha
CoalesceAlpha
ConsistentScatterAlpha
DebugPrinterAlpha
DebugReturnerAlpha
NullBeta
ParallelMapAlpha
ProtectAlpha
QueryCounterAlpha
QueryTypeFilterAlpha
RedisCacheAlpha
RedisClusterPortsRewriteBeta
RedisSinkClusterBeta
RedisSinkSingleBeta
RedisTimestampTaggerAlpha
TeeAlpha
RequestThrottlingAlpha

CassandraSinkCluster

This transform will route Cassandra messages to a node within a Cassandra cluster based on:

  • a configured data_center and rack
  • token aware routing

The fact that Shotover is routing to multiple destination nodes will be hidden from the client. Instead Shotover will pretend to be either a single Cassandra node or part of a cluster of Cassandra nodes consisting entirely of Shotover instances.

This is achieved by rewriting system.local and system.peers/system.peers_v2 query results. The system.local will make Shotover appear to be its own node. While system.peers/system.peers_v2 will be rewritten to list the configured Shotover peers as the only other nodes in the cluster.

- CassandraSinkCluster:
    # contact points must be within the configured data_center and rack.
    # If this is not followed, Shotover will still function correctly but Shotover will communicate with a
    # node outside of the specified data_center and rack.
    first_contact_points: ["172.16.1.2:9042", "172.16.1.3:9042"]

    # A list of every Shotover node that will be proxying to the same Cassandra cluster.
    # This field should be identical for all Shotover nodes proxying to the same Cassandra cluster.
    shotover_nodes:
        # Address of the Shotover node.
        # This is usually the same address as the Shotover source that is connected to this sink.
        # But it may be different if you want Shotover to report a different address.
      - address: "127.0.0.1:9042"
        # The data_center this Shotover node will report as and route messages to.
        # For performance reasons, Shotover should be physically located in this data_center.
        data_center: "dc1"
        # The rack this Shotover node will report as and route messages to.
        # For performance reasons, Shotover should be physically located in this rack.
        rack: "rack1"
        # The host_id that Shotover will report as.
        # Does not affect message routing.
        # Make sure to set this to a unique value for each Shotover node, maybe copy one from: https://wasteaguid.info
        host_id: "2dd022d6-2937-4754-89d6-02d2933a8f7a"

      # If you only have a single Shotover instance then you only want a single node.
      # Otherwise if you have multiple Shotover instances then add more nodes e.g.
      #- address: "127.0.0.2:9042"
      #  data_center: "dc1"
      #  rack: "rack2"
      #  host_id: "3c3c4e2d-ba74-4f76-b52e-fb5bcee6a9f4"
      #- address: "127.0.0.3:9042"
      #  data_center: "dc2"
      #  rack: "rack1"
      #  host_id: "fa74d7ec-1223-472b-97de-04a32ccdb70b"

    # Defines which entry in shotover_nodes this Shotover instance will become.
    # This affects:
    # * the shotover_nodes data_center and rack fields are used for routing messages
    #     + Shotover will never route messages outside of the specified data_center
    #     + Shotover will always prefer to route messages to the specified rack
    #         but may route outside of the rack when nodes in the rack are unreachable
    # * which shotover_nodes entry is included in system.local and excluded from system.peers
    local_shotover_host_id: "2dd022d6-2937-4754-89d6-02d2933a8f7a"

    # Number of milliseconds to wait for a connection to be created to a destination cassandra instance.
    # If the timeout is exceeded then connection to another node is attempted
    # If all known nodes have resulted in connection timeouts an error will be returned to the client.
    connect_timeout_ms: 3000

    # When this field is provided TLS is used when connecting to the remote address.
    # Removing this field will disable TLS.
    #tls:
    #  # Path to the certificate authority file, typically named with a .crt extension.
    #  certificate_authority_path: "tls/localhost_CA.crt"
    #  # Path to the certificate file, typically named with a .crt extension.
    #  certificate_path: "tls/localhost.crt"
    #  # Path to the private key file, typically named with a .key extension.
    #  private_key_path: "tls/localhost.key"
    #  # Enable/disable verifying the hostname of the certificate provided by the destination.
    #  #verify_hostname: true

  # Timeout in seconds after which to give up waiting for a response from the destination.
  # This field is optional, if not provided, timeout will never occur.
  # When a timeout occurs the connection to the client is immediately closed.
  # read_timeout: 60

Error handling

If Shotover sends a request to a node and never gets a response, (maybe the node went down), Shotover will return a Cassandra Server error to the client. This is because the message may or may not have succeded, so only the client can attempt to retry as the retry may involve checking if the original query did in fact complete succesfully.

If no nodes are capable of receiving the query then Shotover will return a Cassandra Overloaded error indicating that the client should retry the query at some point.

All other connection errors will be handled internally by Shotover. And all Cassandra errors will be passed directly back to the client.

Metrics

This transfrom emits a metrics counter named failed_requests and the labels transform defined as CassandraSinkCluster and chain as the name of the chain that this transform is in.

CassandraSinkSingle

This transform will send/receive Cassandra messages to a single Cassandra node. This will just pass the query directly to the remote node. No cluster discovery or routing occurs with this transform.

- CassandraSinkSingle:
    # The IP address and port of the upstream Cassandra node/service.
    remote_address: "127.0.0.1:9042"

    # Number of milliseconds to wait for a connection to be created to the destination cassandra instance.
    # If the timeout is exceeded then an error is returned to the client.
    connect_timeout_ms: 3000

    # When this field is provided TLS is used when connecting to the remote address.
    # Removing this field will disable TLS.
    #tls:
    #  # Path to the certificate authority file, typically named with a .crt extension.
    #  certificate_authority_path: "tls/localhost_CA.crt"
    #  # Path to the certificate file, typically named with a .crt extension.
    #  certificate_path: "tls/localhost.crt"
    #  # Path to the private key file, typically named with a .key extension.
    #  private_key_path: "tls/localhost.key"
    #  # Enable/disable verifying the hostname of the certificate provided by the destination.
    #  #verify_hostname: true

  # Timeout in seconds after which to give up waiting for a response from the destination.
  # This field is optional, if not provided, timeout will never occur.
  # When a timeout occurs the connection to the client is immediately closed.
  # read_timeout: 60

This transfrom emits a metrics counter named failed_requests and the labels transform defined as CassandraSinkSingle and chain as the name of the chain that this transform is in.

CassandraPeersRewrite

This transform should be used with the CassandraSinkSingle transform. It will write over the ports of the peers returned by queries to the system.peers_v2 table in Cassandra with a user supplied value (typically the port that Shotover is listening on so Cassandra drivers will connect to Shotover instead of the Cassandra nodes themselves).

- CassandraPeersRewrite:
    # rewrite the peer ports to 9043
    port: 9043

Coalesce

This transform holds onto messages until some requirement is met and then sends them batched together. Validation will fail if none of the flush_when_ fields are provided, as this would otherwise result in a Coalesce transform that never flushes.

- Coalesce:
    # When this field is provided a flush will occur when the specified number of messages are currently held in the buffer.
    flush_when_buffered_message_count: 2000

    # When this field is provided a flush will occur when the following occurs in sequence:
    # 1. the specified number of milliseconds have passed since the last flush ocurred
    # 2. a new message is received
    flush_when_millis_since_last_flush: 10000

ConsistentScatter

This transform implements a distributed eventual consistency mechanism between the set of defined sub-chains. This transform will wait for a user configurable number of chains to return an OK response before returning the value up-chain. This follows a similar model as used by Cassandra for its consistency model. Strong consistency can be achieved when W + R > RF. In this case RF is always the number of chains in the route_map.

No sharding occurs within this transform and all requests/messages are sent to all routes.

Upon receiving the configured number of responses, the transform will attempt to resolve or unify the response based on metadata about the result. Currently it will try to return the newest response based on a metadata timestamp (last write wins) or it will simply return the largest response if no timestamp information is available.

- ConsistentScatter:
    # The number of chains to wait for a "write" response on.
    write_consistency: 2
    # The number of chains to wait for a "read" response on.
    read_consistency: 2
    # A map of named chains. All chains will be used in each request.
    route_map:
      instance1:
        - CassandraSinkSingle:
            remote_address: "127.0.0.1:9043"
      instance2:
        - CassandraSinkSingle:
            remote_address: "127.1.0.2:9043"
      instance3:
        - CassandraSinkSingle:
            remote_address: "127.2.0.3:9043"

DebugPrinter

This transform will log the query/message at an info level, then call the down-chain transform.

- DebugPrinter

DebugReturner

This transform will drop any messages it receives and return the supplied response.

- DebugReturner
    # return a Redis response
    Redis: "42"
   
    # To intentionally fail, use this variant 
    # Fail

Null

This transform will drop any messages it receives and return an empty response.

- Null

ParallelMap

This transform will send messages in a single batch in parallel across multiple instances of the chain.

If we have a parallelism of 3 then we would have 3 instances of the chain: C1, C2, C3. If the batch then contains messages M1, M2, M3, M4. Then the messages would be sent as follows:

  • M1 would be sent to C1
  • M2 would be sent to C2
  • M3 would be sent to C3
  • M4 would be sent to C1
- ParallelMap:
    # Number of duplicate chains to send messages through.
    parallelism: 1
    # if true then responses will be returned in the same as order as the queries went out.
    # if it is false then response may return in any order.
    ordered_results: true
    # The chain that messages are sent through
    chain:
      - QueryCounter:
          name: "DR chain"
      - RedisSinkSingle:
          remote_address: "127.0.0.1:6379"
          connect_timeout_ms: 3000

Protect

This transform will encrypt specific fields before passing them down-chain, it will also decrypt those same fields from a response. The transform will create a data encryption key on an user defined basis (e.g. per primary key, per value, per table etc).

The data encryption key is encrypted by a key encryption key and persisted alongside the encrypted value (alongside other needed cryptographic material). This transform provides the basis for in-application cryptography with unified key management between datastores. The encrypted value is serialised using bincode and should then be written to a blob field by a down-chain transform.

Fields are protected using ChaCha20-Poly1305. Modification of the field is also detected and raised as an error. DEK protection is dependent on the key manager being used.

Local

- Protect:
    # A key_manager config that configures the protect transform with how to look up keys.
    key_manager:
      Local: 
        kek: Ht8M1nDO/7fay+cft71M2Xy7j30EnLAsA84hSUMCm1k=
        kek_id: ""

    # A mapping of keyspaces, tables and columns to encrypt.
    keyspace_table_columns:
      test_protect_keyspace:
        test_table:
          - col1

AWS

- Protect:
    # A key_manager config that configures the protect transform with how to look up keys.
    key_manager:
      AWSKms:
        endpoint: "http://localhost:5000"
        region: "us-east-1"
        cmk_id: "alias/aws/secretsmanager"
        number_of_bytes: 32
            
    # A mapping of keyspaces, tables and columns to encrypt.
    keyspace_table_columns:
      test_protect_keyspace:
        test_table:
          - col1

Note: Currently the data encryption key ID function is just defined as a static string, this will be replaced by a user defined script shortly.

QueryCounter

This transform will log the queries that pass through it. The log can be accessed via the Shotover metrics

- QueryCounter:
    # this name will be logged with the query count
    name: "DR chain"

This transform emits a metrics counter named query_count with the label name defined as the name from the config, in the example it will be DR chain.

QueryTypeFilter

This transform will drop messages that match the specified filter.

- QueryTypeFilter:
    # drop messages that are read
    filter: Read

    # alternatively:
    #
    # drop messages that are write
    # filter: Write
    #
    # drop messages that are read write
    # filter: ReadWrite
    #
    # drop messages that are schema changes
    # filter: SchemaChange
    #
    # drop messages that are pub sub messages
    # filter: PubSubMessage

RedisCache

This transform will attempt to cache values for a given primary key in a Redis hash set. It is a primarily implemented as a read behind cache. It currently expects an SQL based AST to figure out what to cache (e.g. CQL, PGSQL) and updates to the cache and the backing datastore are performed sequentially.

- RedisCache:
    caching_schema:
      test:
        partition_key: [test]
        range_key: [test]
    chain:
      # The chain can contain anything but must end in a Redis sink
      - RedisSinkSingle:
          # The IP address and port of the upstream redis node/service.
          remote_address: "127.0.0.1:6379"
          connect_timeout_ms: 3000

RedisClusterPortsRewrite

This transform should be used with the RedisSinkCluster transform. It will write over the ports of the nodes returned by CLUSTER SLOTS or CLUSTER NODES with a user supplied value (typically the port that Shotover is listening on so cluster aware Redis drivers will direct traffic through Shotover instead of the nodes themselves).

- RedisClusterPortsRewrite:
    # rewrite the ports returned by `CLUSTER SLOTS` and `CLUSTER NODES` to use this port.
    new_port: 6380

RedisSinkCluster

This transform is a full featured Redis driver that will connect to a Redis cluster and handle all discovery, sharding and routing operations.

- RedisSinkCluster:
    # A list of IP address and ports of the upstream redis nodes/services.
    first_contact_points: ["127.0.0.1:2220", "127.0.0.1:2221", "127.0.0.1:2222", "127.0.0.1:2223", "127.0.0.1:2224", "127.0.0.1:2225"]

    # By default RedisSinkCluster will attempt to emulate a single non-clustered redis node by completely hiding the fact that redis is a cluster.
    # However, when this field is provided, this cluster hiding is disabled.
    # Instead other nodes in the cluster will only be accessed when performing a command that accesses a slot.
    # All other commands will be passed directly to the direct_connection node.
    # direct_connection: "127.0.0.1:2220"

    # The number of connections in the connection pool for each node.
    # e.g. if connection_count is 4 and there are 4 nodes there will be a total of 16 connections.
    # When this field is not provided connection_count defaults to 1.
    connection_count: 1

    # Number of milliseconds to wait for a connection to be created to a destination redis instance.
    # If the timeout is exceeded then connection to another node is attempted
    # If all known nodes have resulted in connection timeouts an error will be returned to the client.
    connect_timeout_ms: 3000

    # When this field is provided TLS is used when connecting to the remote address.
    # Removing this field will disable TLS.
    #tls:
    #  # Path to the certificate authority file, typically named ca.crt.
    #  certificate_authority_path: "tls/ca.crt"
    #  # Path to the certificate file, typically named with a .crt extension.
    #  certificate_path: "tls/redis.crt"
    #  # Path to the private key file, typically named with a .key extension.
    #  private_key_path: "tls/redis.key"
    #  # Enable/disable verifying the hostname of the certificate provided by the destination.
    #  #verify_hostname: true

Unlike other Redis cluster drivers, this transform does support pipelining. It does however turn each command from the pipeline into a group of requests split between the master Redis node that owns them, buffering results as within different Redis nodes as needed. This is done sequentially and there is room to make this transform split requests between master nodes in a more concurrent manner.

Latency and throughput will be different from pipelining with a single Redis node, but not by much.

This transfrom emits a metrics counter named failed_requests and the labels transform defined as RedisSinkCluster and chain as the name of the chain that this transform is in.

Differences to real Redis

On an existing authenticated connection, a failed auth attempt will not "unauthenticate" the user. This behaviour matches Redis 6 but is different to Redis 5.

Completeness

Note: Currently RedisSinkcluster does not support the following functionality:

  • Redis Transactions
  • Scan based operations e.g. SSCAN

RedisSinkSingle

This transform will take a query, serialise it into a RESP2 compatible format and send to the Redis compatible database at the defined address.

- RedisSinkSingle:
    # The IP address and port of the upstream redis node/service.
    remote_address: "127.0.0.1:6379"

    # Number of milliseconds to wait for a connection to be created to the destination redis instance.
    # If the timeout is exceeded then an error is returned to the client.
    connect_timeout_ms: 3000

    # When this field is provided TLS is used when connecting to the remote address.
    # Removing this field will disable TLS.
    #tls:
    #  # Path to the certificate authority file, typically named ca.crt.
    #  certificate_authority_path: "tls/ca.crt"
    #  # Path to the certificate file, typically named with a .crt extension.
    #  certificate_path: "tls/redis.crt"
    #  # Path to the private key file, typically named with a .key extension.
    #  private_key_path: "tls/redis.key"
    #  # Enable/disable verifying the hostname of the certificate provided by the destination.
    #  #verify_hostname: true

Note: this will just pass the query to the remote node. No cluster discovery or routing occurs with this transform.

This transfrom emits a metrics counter named failed_requests and the labels transform defined as RedisSinkSingle and chain as the name of the chain that this transform is in.

RedisTimestampTagger

A transform that wraps each Redis command in a Lua script that also fetches the key for the operations idletime. This is then used to build a last modified timestamp and insert it into a response's timestamp. The response from the Lua operation is unwrapped and returned to up-chain transforms looking like a normal Redis response.

This is mainly used in conjunction with the ConsistentScatter transform to enable a Cassandra style consistency model within Redis.

- RedisTimestampTagger

Tee

This transform sends messages to both the defined sub chain and the remaining down-chain transforms. The response from the down-chain transform is returned back up-chain but various behaviours can be defined by the behaviour field to handle the case when the responses from the sub chain and down-chain do not match.

- Tee:
    # Ignore responses returned by the sub chain
    behavior: Ignore

    # Alternatively:
    #
    # If the responses returned by the sub chain do not equal the responses returned by down-chain then return an error.
    # behavior: FailOnMismatch
    #
    # If the responses returned by the sub chain do not equal the responses returned by down-chain,
    # then the original message is also sent down the SubchainOnMismatch sub chain.
    # This is useful for logging failed messages.
    # behavior: 
    #   SubchainOnMismatch:
    #     - QueryTypeFilter:
    #         filter: Read
    #     - Null

    # Timeout for sending to the sub chain in microseconds
    timeout_micros: 1000
    # The number of message batches that the tee can hold onto in its buffer of messages to send.
    # If they arent sent quickly enough and the buffer is full then tee will drop new incoming messages.
    buffer_size: 10000
    # The sub chain to send duplicate messages through
    chain:
      - QueryTypeFilter:
          filter: Read
      - Null

This transfrom emits a metrics counter named tee_dropped_messages and the label chain as Tee.

RequestThrottling

This transform will backpressure requests to Shotover, ensuring that throughput does not exceed the max_requests_per_second value.max_requests_per_second has a minimum allowed value of 50 to ensure that drivers such as Cassandra are able to complete their startup procedure correctly. In Shotover, a "request" is counted as a query/statement to upstream service. In Cassandra, the list of queries in a BATCH statement are each counted as individual queries. It uses a Generic Cell Rate Algorithm.

- RequestThrottling
    max_requests_per_second: 20000