solution: config option to disable an upstream

docs/reference-configuration.adoc

@@ -616,6 +616,11 @@ Fallback role mean that the upstream is used only after other upstreams failed o
 Cluster may have multiple upstreams for a single blockchain.
 Accepted types: `bitcoin`, `bitcoin-testnet`, `ethereum`, `ethereum-classic`, `kovan-testnet`, `rinkeby-testnet`, `ropsten-testnet`, or `goerli-testnet`
 
+| `enabled`
+| no
+| `true` (default) or `false`.
+Enable/disable the upstream.
+
 | `labels`
 | no
 | Key-Value pairs that are assigned to the upstream.

src/main/kotlin/io/emeraldpay/dshackle/config/UpstreamsConfigReader.kt

@@ -194,6 +194,9 @@ class UpstreamsConfigReader(
         upstream.id = getValueAsString(upNode, "id")
         upstream.options = tryReadOptions(upNode)
         upstream.methods = tryReadMethods(upNode)
+        getValueAsBool(upNode, "enabled")?.let {
+            upstream.isEnabled = it
+        }
     }
 
     internal fun readUpstreamGrpc(

src/main/kotlin/io/emeraldpay/dshackle/startup/ConfiguredUpstreams.kt

@@ -63,6 +63,10 @@ open class ConfiguredUpstreams(
         log.debug("Starting upstreams")
         val defaultOptions = buildDefaultOptions(config)
         config.upstreams.forEach { up ->
+            if (!up.isEnabled) {
+                log.debug("Upstream ${up.id} is disabled")
+                return@forEach
+            }
             log.debug("Start upstream ${up.id}")
             if (up.connection is UpstreamsConfig.GrpcConnection) {
                 val options = up.options ?: UpstreamsConfig.Options()