SSL Handshake timeout error for more than 1000 concurrent calls to snowplow stream collector in GCP

We have setup snowplow stream collector in GCP Kubernetes cluster with load balancer. We are load testing for more than 1000 concurrent users are sending events to collector endpoint using Gatling. During test execution, it is throwing below errors :
1. connection timed out
2. SSLException: handshake timed out

In Kubernetes, our application is deployed in replica-set(deployment) with HPA, also nodes are scalable, application is accessed via load balancer(HTTP) with google manage ssl certificate with ingress controller(type GCP).

I want to know if there is any limit on maximum number of parallel connections accepted.
Also, below is the configuration used for collector.

# 'collector' contains configuration options for the main Scala collector.
collector {
  # The collector runs as a web service specified on the following interface and port.
  interface = ""
  interface = ${?COLLECTOR_INTERFACE}
  port = 8080
  port = ${?COLLECTOR_PORT}

  # optional SSL/TLS configuration
  ssl {
    enable = false
    enable = ${?COLLECTOR_SSL}
    # whether to redirect HTTP to HTTPS
    redirect = false
    redirect = ${?COLLECTOR_SSL_REDIRECT}
    port = 443
    port = ${?COLLECTOR_SSL_PORT}

  # The collector responds with a cookie to requests with a path that matches the 'vendor/version' protocol.
  # The expected values are:
  # - com.snowplowanalytics.snowplow/tp2 for Tracker Protocol 2
  # - r/tp2 for redirects
  # - com.snowplowanalytics.iglu/v1 for the Iglu Webhook
  # Any path that matches the 'vendor/version' protocol will result in a cookie response, for use by custom s
  # downstream of the collector.
  # But you can also map any valid (i.e. two-segment) path to one of the three defaults.
  # Your custom path must be the key and the value must be one of the corresponding default paths. Both must be full
  # valid paths starting with a leading slash.
  # Pass in an empty map to avoid mapping.
  paths {
    # "/com.acme/track" = "/com.snowplowanalytics.snowplow/tp2"
    # "/com.acme/redirect" = "/r/tp2"
    # "/com.acme/iglu" = "/com.snowplowanalytics.iglu/v1"

  # Configure the P3P policy header.
  p3p {
    policyRef = "/w3c/p3p.xml"

  # Cross domain policy configuration.
  # If "enabled" is set to "false", the collector will respond with a 404 #to the /crossdomain.xml
  # route.
  crossDomain {
    enabled = false
    # Domains that are granted access, * will match and
    domains = [ "*" ]
    # Whether to only grant access to HTTPS or both HTTPS and HTTP sources
    secure = true

  # The collector returns a cookie to clients for user identification
  # with the following domain and expiration.
  cookie {
    enabled = true
    # enabled = ${?COLLECTOR_COOKIE_ENABLED}
    expiration = "365 days" # e.g. "365 days"
    # expiration = ${?COLLECTOR_COOKIE_EXPIRATION}
    # Network cookie name
    name = ncm
    # name = ${?COLLECTOR_COOKIE_NAME}
    # The domain is optional and will make the cookie accessible to other
    # applications on the domain. Comment out these lines to tie cookies to
    # the collector's full domain.
    # The domain is determined by matching the domains from the Origin header of the request
    # to the list below. The first match is used. If no matches are found, the fallback domain will be used,
    # if configured.
    # If you specify a main domain, all subdomains on it will be matched.
    # If you specify a subdomain, only that subdomain will be matched.
    # Examples:
    # will match, and
    # will match but not or
    #domains = [
    #   "{{cookieDomain1}}" # e.g. "" -> any origin domain ending with this will be matched and will be returned
    #    "{{cookieDomain2}}" # e.g. "" -> any origin domain ending with this will be matched and will be returned
        # ... more domains
    # domains += ${?COLLECTOR_COOKIE_DOMAIN_1}
    # domains += ${?COLLECTOR_COOKIE_DOMAIN_2}
    # # ... more domains
    # # If specified, the fallback domain will be used if none of the Origin header hosts matches the list of
    # # cookie domains configured above. (For example, if there is no Origin header.)
    # fallbackDomain = "{{fallbackDomain}}"
    # fallbackDomain = ${?FALLBACK_DOMAIN}
    secure = false
    httpOnly = false
    # # The sameSite is optional. You can choose to not specify the attribute, or you can use `Strict`,
    # # `Lax` or `None` to limit the cookie sent context.
    # #   Strict: the cookie will only be sent along with "same-site" requests.
    # #   Lax: the cookie will be sent with same-site requests, and with cross-site top-level navigation.
    # #   None: the cookie will be sent with same-site and cross-site requests.
    # sameSite = "{{cookieSameSite}}"

  # If you have a do not track cookie in place, the Scala Stream Collector can respect it by
  # completely bypassing the processing of an incoming request carrying this cookie, the collector
  # will simply reply by a 200 saying "do not track".
  # The cookie name and value must match the configuration below, where the names of the cookies must
  # match entirely and the value could be a regular expression.
  doNotTrackCookie {
    enabled = false
    name = ""
    value = ""

  # When enabled and the cookie specified above is missing, performs a redirect to itself to check
  # if third-party cookies are blocked using the specified name. If they are indeed blocked,
  # fallbackNetworkId is used instead of generating a new random one.
  cookieBounce {
    enabled = false
    # The name of the request parameter which will be used on redirects checking that third-party
    # cookies work.
    name = "n3pc"
    # Network user id to fallback to when third-party cookies are blocked.
    fallbackNetworkUserId = "00000000-0000-4000-A000-000000000000"
    # # Optionally, specify the name of the header containing the originating protocol for use in the
    # # bounce redirect location. Use this if behind a load balancer that performs SSL termination.
    # The value of this header must be http or https. Example, if behind an AWS Classic ELB.
    forwardedProtocolHeader = "X-Forwarded-Proto"

  # When enabled, redirect prefix `r/` will be enabled and its query parameters resolved.
  # Otherwise the request prefixed with `r/` will be dropped with `404 Not Found`
  # Custom redirects configured in `paths` can still be used.
  enableDefaultRedirect = true
  enableDefaultRedirect = ${?COLLECTOR_ALLOW_REDIRECTS}

  # When enabled, the redirect url passed via the `u` query parameter is scanned for a placeholder
  # token. All instances of that token are replaced withe the network ID. If the placeholder isn't
  # specified, the default value is `${SP_NUID}`.
  redirectMacro {
    enabled = false
    # # Optional custom placeholder token (defaults to the literal `${SP_NUID}`)
    placeholder = "[TOKEN]"

  # Customize response handling for requests for the root path ("/").
  # Useful if you need to redirect to web content or privacy policies regarding the use of this collector.
  rootResponse {
    enabled = false
    statusCode = 302
    # Optional, defaults to empty map
    headers = {
      Location = "",
      X-Custom = "something"
    # # Optional, defaults to empty string
    body = "302, redirecting"

  # Configuration related to CORS preflight requests
  cors {
    # The Access-Control-Max-Age response header indicates how long the results of a preflight
    # request can be cached. -1 seconds disables the cache. Chromium max is 10m, Firefox is 24h.
    accessControlMaxAge = 5 seconds

  # Configuration of prometheus http metrics
  prometheusMetrics {
    # If metrics are enabled then all requests will be logged as prometheus metrics
    # and '/metrics' endpoint will return the report about the requests
    enabled = false
    # Custom buckets for http_request_duration_seconds_bucket duration metric
    #durationBucketsInSeconds = [0.1, 3, 10]

  streams {
    # Events which have successfully been collected will be stored in the good stream/topic
    good = "good"

    # Bad rows ( will be stored in the bad stream/topic.
    # The collector can currently produce two flavours of bad row:
    #  - a size_violation if an event is larger that the Kinesis (1MB) or SQS (256KB) limits;
    #  - a generic_error if a request's querystring cannot be parsed because of illegal characters
    bad = "bad"

    # Whether to use the incoming event's ip as the partition key for the good stream/topic
    # Note: Nsq does not make use of partition key.
    useIpAddressAsPartitionKey = false

    # Enable the chosen sink by uncommenting the appropriate configuration
    sink {
      # Choose between kinesis, sqs, google-pub-sub, kafka, nsq, or stdout.
      # To use stdout, comment or remove everything in the "collector.streams.sink" section except
      # "enabled" which should be set to "stdout".
      enabled = "google-pub-sub" # or sqs

      # Region where the streams are located
      #region = {{kinesisRegion}} # or {{sqsRegion}}
      region = 'us'

      ## Optional endpoint url configuration to override aws kinesis endpoints,
      ## this can be used to specify local endpoints when using localstack
      # customEndpoint = {{kinesisEndpoint}}

      # Thread pool size for Kinesis and SQS API requests
      threadPoolSize = 10

      # Optional SQS buffer for good and bad events (respectively).
      # When messages can't be sent to Kinesis, they will be sent to SQS.
      # If not configured, sending to Kinesis will be retried.
      # This should only be set up for the Kinesis sink, where it acts as a failsafe.
      # For the SQS sink, the good and bad queue should be specified under streams.good and streams.bad, respectively and these settings should be ignored.
    #   sqsGoodBuffer = {{sqsGoodBuffer}}

    #   sqsBadBuffer = {{sqsBadBuffer}}

      # The following are used to authenticate for the Amazon Kinesis and SQS sinks.
      # If both are set to 'default', the default provider chain is used
      # (see
      # If both are set to 'iam', use AWS IAM Roles to provision credentials.
      # If both are set to 'env', use environment variables AWS_ACCESS_KEY_ID and AWS_SECRET_ACCESS_KEY
      # aws {
      #   accessKey = iam
      #   secretKey = iam
      # }

      # # Minimum and maximum backoff periods, in milliseconds
    #   backoffPolicy {
    #     minBackoff = 2000
    #     maxBackoff = 5000
    #   }

      # Or Google Pubsub
      googleProjectId = tc-sc-bi-bigdata-cksm-dp-dev
      # Minimum, maximum and total backoff periods, in milliseconds
      # and multiplier between two backoff
      backoffPolicy {
       minBackoff = 5000
       maxBackoff = 9000
       totalBackoff = 11000 # must be >= 10000
       multiplier = 1

      # Or Kafka
      #brokers = "{{kafkaBrokers}}"
      ## Number of retries to perform before giving up on sending a record
      #retries = 0
      # The kafka producer has a variety of possible configuration options defined at
      # Some values are set to other values from this config by default:
      # "bootstrap.servers" = brokers
      # "buffer.memory"     = buffer.byteLimit
      # ""         = buffer.timeLimit
      producerConf {
        acks = all
      #  "key.serializer"     = "org.apache.kafka.common.serialization.StringSerializer"
      #  "value.serializer"   = "org.apache.kafka.common.serialization.StringSerializer"


    #Incoming events are stored in a buffer before being sent to Kinesis/Kafka.
    #Note: Buffering is not supported by NSQ.
    #The buffer is emptied whenever:
    #- the number of stored records reaches record-limit or
    #- the combined size of the stored records reaches byte-limit or
    #- the time in milliseconds since the buffer was last emptied reaches time-limit
    buffer {
      byteLimit = 2000000 
      recordLimit = 100 # Not supported by Kafka; will be ignored
      timeLimit = 1000
  # Telemetry sends heartbeat events to external pipeline.
  # Unless disable parameter set to true, this feature will be enabled. Deleting whole section will not disable it.
  # Schema URI: iglu:com.snowplowanalytics.oss/oss_context/jsonschema/1-0-1
  telemetry {
      disable = false
      interval = 60 minutes

      # Connection properties for the receiving pipeline
      method = POST
      url =
      port = 443
      secure = true

      # User provided tracking details
      applicationName: "snowplow-test"
      applicationVersion: 1

      # Deployment settings are populated by the rollout scripts. Should not be manually modified.
    #   userProvidedId = {{userProvidedId}}
    #   moduleName = {{moduleName}}
    #   moduleVersion = {{moduleVersion}}
    #   instanceId = {{instanceId}}
    #   autoGeneratedId = {{autoGeneratedId}}

akka {
  loglevel = DEBUG # 'OFF' for no logging, 'DEBUG' for all logging.
  loglevel = ${?AKKA_LOGLEVEL}
  loggers = ["akka.event.slf4j.Slf4jLogger"]
  loggers = [${?AKKA_LOGGERS}]

  # akka-http is the server the Stream collector uses and has configurable options defined at
  http.server {
    # To obtain the hostname in the collector, the 'remote-address' header
    # should be set. By default, this is disabled, and enabling it
    # adds the 'Remote-Address' header to every request automatically.
    remote-address-header = on
    remote-address-header = ${?AKKA_HTTP_SERVER_REMOTE_ADDRESS_HEADER}

    raw-request-uri-header = on
    raw-request-uri-header = ${?AKKA_HTTP_SERVER_RAW_REQUEST_URI_HEADER}

    # Define the maximum request length (the default is 2048)
    parsing {
      max-uri-length = 32768
      max-uri-length = ${?AKKA_HTTP_SERVER_PARSING_MAX_URI_LENGTH}
      uri-parsing-mode = relaxed
      uri-parsing-mode = ${?AKKA_HTTP_SERVER_PARSING_URI_PARSING_MODE}

Let us know if you want more context on the same.

Hi @Atanu_Sankar_Kundu - there is indeed an Akka HTTP open connections limit default which might be at play here.


akka.http.server.max-connections = <SOME NUMBER HERE>

By default this is limited to 1024 which could be why you are hitting issues - though that is per pod. Would recommend bumping that a higher number that fits the CPU / Memory allocation you have given to the pod.


Thank you so much @josh, this was helpful. We are working on the issue. In case we face any other blocker we will reach out to you.

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