telegraf.conf

# Run cassandra with Jolokia to expose JMX metrics over HTTP
# Add the following to /etc/cassandra/cassandra-env.sh
JVM_OPTS="$JVM_OPTS -javaagent:/opt/jolokia/jolokia-jvm-agent.jar"

# See https://www.flexinvesting.fi/2014/jolokia-apache-cassandra/
# for more information.

# Collect information with Telegraf according to the below config.
# There's also a http json plugin that should be useful for fetching
# information from arbitrary HTTP JSON interfaces.

############### Telegraf config file #######################

# Tags can also be specified via a normal map, but only one form at a time:
[tags]
  # dc = "us-east-1"

# Configuration for telegraf agent
[agent]
  # Default data collection interval for all inputs
  interval = "10s"
  # Rounds collection interval to 'interval'
  # ie, if interval="10s" then always collect on :00, :10, :20, etc.
  round_interval = true

  # Default data flushing interval for all outputs. You should not set this below
  # interval. Maximum flush_interval will be flush_interval + flush_jitter
  flush_interval = "10s"
  # Jitter the flush interval by a random amount. This is primarily to avoid
  # large write spikes for users running a large number of telegraf instances.
  # ie, a jitter of 5s and interval 10s means flushes will happen every 10-15s
  flush_jitter = "0s"

  # Run telegraf in debug mode
  debug = false
  # Run telegraf in quiet mode
  quiet = false
  # Override default hostname, if empty use os.Hostname()
  hostname = ""


###############################################################################
#                                  OUTPUTS                                    #
###############################################################################



# Configuration for influxdb server to send metrics to
[[outputs.influxdb]]
  # The full HTTP or UDP endpoint URL for your InfluxDB instance.
  # Multiple urls can be specified but it is assumed that they are part of the same
  # cluster, this means that only ONE of the urls will be written to each interval.
  # urls = ["udp://localhost:8089"] # UDP endpoint example
  urls = ["http://localhost:8086"] # required
  # The target database for metrics (telegraf will create it if not exists)
  database = "telegraf" # required
  # Precision of writes, valid values are n, u, ms, s, m, and h
  # note: using second precision greatly helps InfluxDB compression
  precision = "s"

  # Connection timeout (for the connection with InfluxDB), formatted as a string.
  # If not provided, will default to 0 (no timeout)
  # timeout = "5s"
  # username = "telegraf"
  # password = "metricsmetricsmetricsmetrics"
  # Set the user agent for HTTP POSTs (can be useful for log differentiation)
  # user_agent = "telegraf"
  # Set UDP payload size, defaults to InfluxDB UDP Client default (512 bytes)
  # udp_payload = 512

###############################################################################
#                                  INPUTS                                     #
###############################################################################


# Inserts sine and cosine waves for demonstration purposes
[[inputs.Trig]]
  # Set the amplitude
  amplitude = 10.0


# Read metrics about cpu usage
[[inputs.cpu]]
  # Whether to report per-cpu stats or not
  percpu = true
  # Whether to report total system cpu stats or not
  totalcpu = true
  # Comment this line if you want the raw CPU time metrics
  drop = ["time_*"]

# Read metrics about disk usage by mount point
[[inputs.disk]]
  # By default, telegraf gather stats for all mountpoints.
  # Setting mountpoints will restrict the stats to the specified mountpoints.
  # Mountpoints=["/"]

# Read metrics about disk IO by device
[[inputs.diskio]]
  # By default, telegraf will gather stats for all devices including
  # disk partitions.
  # Setting devices will restrict the stats to the specified devcies.
  # devices = ["sda","sdb"]
  # Uncomment the following line if you do not need disk serial numbers.
  # skip_serial_number = true


# Read InfluxDB-formatted JSON metrics from one or more HTTP endpoints
[[inputs.influxdb]]
  # Works with InfluxDB debug endpoints out of the box,
  # but other services can use this format too.
  # See the influxdb plugin's README for more details.

  # Multiple URLs from which to read InfluxDB-formatted JSON
  urls = [
    "http://localhost:8086/debug/vars"
  ]


[[inputs.jolokia]]
  # This is the context root used to compose the jolokia url
  context = "/jolokia/read"

  # List of servers exposing jolokia read service
  [[inputs.jolokia.servers]]
    name = "stable"
    host = "localhost"
    port = "8778"
    # username = "myuser"
    # password = "mypassword"

  # List of metrics collected on above servers
  # Each metric consists in a name, a jmx path and either a pass or drop slice attributes
  # This collect all heap memory usage metrics
  [[inputs.jolokia.metrics]]
    name = "heap_memory_usage"
    jmx  = "/java.lang:type=Memory/HeapMemoryUsage"


# Read metrics about memory usage
[[inputs.mem]]
  # no configuration

# Read metrics about network interface usage
[[inputs.net]]
  # By default, telegraf gathers stats from any up interface (excluding loopback)
  # Setting interfaces will tell it to gather these explicit interfaces,
  # regardless of status.
  #
  # interfaces = ["eth0", ... ]

# Read metrics about TCP status such as established, time wait etc and UDP sockets counts.
[[inputs.netstat]]
  # no configuration


# Ping given url(s) and return statistics
[[inputs.ping]]
  # urls to ping
  urls = ["www.google.com"] # required
  # number of pings to send (ping -c <COUNT>)
  count = 1 # required
  # interval, in s, at which to ping. 0 == default (ping -i <PING_INTERVAL>)
  ping_interval = 0.0
  # ping timeout, in s. 0 == no timeout (ping -t <TIMEOUT>)
  timeout = 0.0
  # interface to send ping from (ping -I <INTERFACE>)
  interface = ""

I've been working on this same approach too. Have a look: https://github.com/chrusty/telegraf-cassandra
This is working quite well, but I'm still looking for a clean solution to monitor individual tables.