I've got the following configuration:
Redis_version:3.2.0
3 master nodes and 3 slave nodes
Each master node is replicated to a slave Everything is correct. When one master node fails by a "kill" command, the corresponding slave node becomes the master as expected. After few seconds, cluster_state returns to the OK state.
BUT, if two master nodes fail simultaneously, none of the associated slave nodes become the master. The cluster_state stays in "fail" state.
cluster nodes command output.
b60c284a515b31aa6b11022fc07cf1a399171e04 127.0.0.1:7000 master,fail? - 1464690455030 1464690454930 1 disconnected 0-5460
637d1f074419963653b206c5ed7cbed4c3d0ace0 127.0.0.1:7001 master,fail? - 1464690455030 1464690454930 2 disconnected 5461-10922
d2aae2a3d87c6407e002076740c8febf80f37865 127.0.0.1:7003 myself,slave b60c284a515b31aa6b11022fc07cf1a399171e04 0 0 4 connected
72d4c9ce140fb57436c1b21702bf3c646ef29db3 127.0.0.1:7002 master - 0 1464690718480 3 connected 10923-16383
af34a7b2241943baf23e634e81b552d8bf23cdd0 127.0.0.1:7005 slave 72d4c9ce140fb57436c1b21702bf3c646ef29db3 0 1464690718480 6 connected
d0fec0609c9e786ac9ca4629f36cabd7c5c3130c 127.0.0.1:7004 slave 637d1f074419963653b206c5ed7cbed4c3d0ace0 0 1464690718480 5 connected
The slave auto-failover won't happen when at least half of the masters get disconnected, because the failover election is required more than half of the masters come into consensus.
To start a manual failover, connect to the slave node with redis-cli and send a cluster failover TAKEOVER command (the takeover is required).
In your case
redis-cli -h 127.0.0.1 -p 7003 cluster failover takeover
After the :7003 becomes a master, the other slave will start an automatic failover as well since there are more than half (2/3) of the masters are alive.
Related
According to official docs of ClickHouse there's the request for monitoring that could inform me if something wrong with my replica.
SELECT
database,
table,
is_leader,
is_readonly,
is_session_expired,
future_parts,
parts_to_check,
columns_version,
queue_size,
inserts_in_queue,
merges_in_queue,
log_max_index,
log_pointer,
total_replicas,
active_replicas
FROM system.replicas
WHERE
is_readonly
OR is_session_expired
OR future_parts > 20
OR parts_to_check > 10
OR queue_size > 20
OR inserts_in_queue > 10
OR log_max_index - log_pointer > 10
OR total_replicas < 2
OR active_replicas < total_replicas
Have I additionaly monitoring leader state of my replica? What happens with replica if leader get down and there's no one node which could be leader instead (can_become_leader: 0)?
What happens with replica if leader get down and there's no one node which could be leader instead (can_become_leader: 0)?
Merges and mutations will stop. You will get the error "too many parts".
So, we have a Redis cluster mode enabled up and running in an EC2 instance(can't use the AWS managed one) and to connect to it from our internal network we are announcing our IP and Port using cluster-announce-ip,cluster-announce-port and cluster-bus-port where the IP announced is accessible from our network.
It seems to be working fine but not stable i.e. it keeps on switching between the IP provided and the loopback address, see below:
internal:36379> cluster nodes
eec09ffe56b05ad12b615b1d72fb6759f9c442dd internal:36379#40002 slave,fail b48e9381bfc8870317890483f3a610195a88c726 1580294719147 1580294718345 8 connected
ca0cb878becba2270cf00ec75be806304d561b0b internal:36379#40003 slave 3a5c9bc26bb3fbc7e850199320595946f3a6569a 1580294720250 1580294719347 9 connected
3a5c9bc26bb3fbc7e850199320595946f3a6569a internal:30006#40006 myself,master - 0 1580294720000 9 connected 10923-16383
33de5143f47674dd0fc636404fe4d7752d2cf9e2 internal:36379#40004 master - 1580294720651 1580294720151 7 connected 0-5460
b48e9381bfc8870317890483f3a610195a88c726 internal:36379#40005 master,fail - 1580294721253 1580294721153 8 connected 5461-10922
74cd3e1ededd204408e2dabce022bd08ab6b03b3 internal:36379#40001 slave,fail 33de5143f47674dd0fc636404fe4d7752d2cf9e2 1580215532177 1580215531374 7 connected
internal:36379>
internal:36379> cluster nodes
eec09ffe56b05ad12b615b1d72fb6759f9c442dd 127.0.0.1:30002#40002 slave b48e9381bfc8870317890483f3a610195a88c726 0 1580294727000 8 connected
ca0cb878becba2270cf00ec75be806304d561b0b 127.0.0.1:30003#40003 slave 3a5c9bc26bb3fbc7e850199320595946f3a6569a 0 1580294727381 9 connected
3a5c9bc26bb3fbc7e850199320595946f3a6569a internal:30006#40006 myself,master - 0 1580294726000 9 connected 10923-16383
33de5143f47674dd0fc636404fe4d7752d2cf9e2 internal:36379#40004 master,fail? - 1580294725274 1580294725000 7 connected 0-5460
b48e9381bfc8870317890483f3a610195a88c726 127.0.0.1:30005#40005 master,fail - 0 1580294727080 8 connected 5461-10922
74cd3e1ededd204408e2dabce022bd08ab6b03b3 internal:36379#40001 slave,fail 33de5143f47674dd0fc636404fe4d7752d2cf9e2 1580215532177 1580215531374 7 connected
internal:36379>
Where internal is one of our six internal IPs.Originally cluster is running on ports 30001-30006.We are able to set/get keys momentarily before it switches back to announcing the local address instead of our IP.
Any idea why this is not stable?
Two Node cluster Node A , Node B .
Service X running on Node A, Node B is DC.
We are using stack corosync with Pacemaker.
Failure Timeout is 10 sec .
Target-Role is started .
Events happens like this
Node A sends event to Node B Service X is down
Node B prints Ignoring expired failure for Service X
After this Service X is never restarted by the Cluster.
Now questions are:
Why is Node B (DC) ignoring the expired failure?
Even for this time DC ignored but as the Service X is down, Node A should monitor the service and again send failure status to Node B and at that time Node B should restart the service. Why this no hapenning?
One Reason for this may be time difference between two servers (DC and Other Machine) .
So , DC thinks that this event is old and ignore it . Please sync time and then try to re-create the issue .
U can add the following property to your crm configuration which will try to start failed, expired resources.
start-failure-is-fatal="false"
We are trying to run a cassandra cluster on AWS/EC2 within a standard VPC footprint (cassandra nodes on private subnets). Because this is AWS there is always a chance that an EC2 instance will terminate or reboot with no warning. I have been simulating this case on a test cluster and I am seeing things with the cluster that I thought a cluster was suppose to prevent. Specifically if a node reboots some data will go temporarily missing until the node completes its reboot. If a node terminates it appears that some data is lost forever.
For my test I just did a bunch of writes (using QUORUM consistency) to some keyspaces then interrogate the contents of those keyspaces as I bring down nodes (either through reboot or terminate). I'm just using cqlsh SELECT to do the keyspace/column family interrogation of the cluster using ONE consistency level.
Note, even though I am performing no writes to the cluster while I am doing the SELECTs rows temporarily disappear when rebooting and can permanently go missing during termination.
I thought Netflix Priam might be able to help, but sadly it doesn't work in a VPC the last time I checked.
Also, because we are using ephemeral storage instances there is no equivalent of 'shutdown' so I cannot run any scripts during reboot/terminate of an instance to perform a nodetool decommission or nodetool removenode before an instance goes away. Terminate is the equivalent of kicking the plug out of the wall.
Since I am using a replication factor of 3 and quorum/write that should mean that all data is written to at least 2 nodes. So, unless I am totally misunderstanding things (which is possible), losing one node should not mean that I lose any data for any period of time when I am using consistency level ONE for the read.
Questions
Why wouldn't a 6 node cluster with a replication factor of 3 work?
Do I need to run something like a 12 node cluster with a replication factor of 7? Don't bother telling me that will fix the problem, because it doesn't.
Do I need to use consistency level of ALL on the writes then use ONE or QUORUM on the reads?
Is there something not quite right with virtual nodes? unlikely
Are there nodetool commands besides removenode that I need to run when a node terminates to recover missing data? As mentioned earlier, when a reboot occurs, eventually the missing data reappears.
Is there some cassandra savant who can look at my cassandra.yaml file below and send me on the path to salvation?
More Info added 7/19
I don't think this is a QUORUM vs ONE vs ALL is the issue. The test I set up performs no writes to the keyspaces after the initial population of the column families. So the data has had plenty of time (hours) to make it to all the nodes as required by the replication factor. Plus the test dataset is REALLY small (2 column families with about 300-1000 values each). So in other words, the data is completely static.
The behavior I am seeing seems to be tied to the fact that the ec2 instance is no longer on the network. The reason I say this is because if I log on to a node and just do a cassandra stop I see no loss of data. But if I do the reboot or terminate I start getting the following in a stack trace.
CassandraHostRetryService - Downed Host Retry service started with queue size -1 and retry delay 10s
CassandraHostRetryService - Downed Host retry shutdown complete
CassandraHostRetryService - Downed Host retry shutdown hook called
Caused by: TimedOutException()
Caused by: TimedOutException()
So it seems to be more of a networking communication issue in that the cluster is expecting, for example 10.0.12.74, to be on the network after it has joined the cluster. If that ip is suddenly unreachable either due to reboot or termination the timeouts start happening.
When I do a nodetool status under all three scenarios (cassandra stop, reboot or terminate) the status of the node shows up as DN. Which is what you would expect. Eventually nodetool status will return to UN with cassandra start or reboot, but obviously termination always stays DN.
Details of my Configuration
Here are some details of my configuration (cassandra.yaml is at the bottom of this posting):
Nodes are running in private subnets of a VPC.
Cassandra 1.2.5 with num_tokens: 256 (virtual nodes). initial_token: (blank). I am really hoping this works because all of our nodes run in autoscaling groups so the thought that redistribution could be handle dynamically is appealing.
EC2 m1.large one seed and one non-seed node in each availability zone. (so 6 total nodes in the cluster).
Ephemeral storage, not EBS.
Ec2Snitch with NetworkTopologyStrategy and all keyspaces have replication factor of 3.
Non-seed nodes are auto_bootstraped, seed nodes are not.
sample cassandra.yaml file
cluster_name: 'TestCluster'
num_tokens: 256
initial_token:
hinted_handoff_enabled: true
max_hint_window_in_ms: 10800000
hinted_handoff_throttle_in_kb: 1024
max_hints_delivery_threads: 2
authenticator: org.apache.cassandra.auth.AllowAllAuthenticator
authorizer: org.apache.cassandra.auth.AllowAllAuthorizer
partitioner: org.apache.cassandra.dht.Murmur3Partitioner
disk_failure_policy: stop
key_cache_size_in_mb:
key_cache_save_period: 14400
row_cache_size_in_mb: 0
row_cache_save_period: 0
row_cache_provider: SerializingCacheProvider
saved_caches_directory: /opt/company/dbserver/caches
commitlog_sync: periodic
commitlog_sync_period_in_ms: 10000
commitlog_segment_size_in_mb: 32
seed_provider:
- class_name: org.apache.cassandra.locator.SimpleSeedProvider
parameters:
- seeds: "SEED_IP_LIST"
flush_largest_memtables_at: 0.75
reduce_cache_sizes_at: 0.85
reduce_cache_capacity_to: 0.6
concurrent_reads: 32
concurrent_writes: 8
memtable_flush_queue_size: 4
trickle_fsync: false
trickle_fsync_interval_in_kb: 10240
storage_port: 7000
ssl_storage_port: 7001
listen_address: LISTEN_ADDRESS
start_native_transport: false
native_transport_port: 9042
start_rpc: true
rpc_address: 0.0.0.0
rpc_port: 9160
rpc_keepalive: true
rpc_server_type: sync
thrift_framed_transport_size_in_mb: 15
thrift_max_message_length_in_mb: 16
incremental_backups: true
snapshot_before_compaction: false
auto_bootstrap: AUTO_BOOTSTRAP
column_index_size_in_kb: 64
in_memory_compaction_limit_in_mb: 64
multithreaded_compaction: false
compaction_throughput_mb_per_sec: 16
compaction_preheat_key_cache: true
read_request_timeout_in_ms: 10000
range_request_timeout_in_ms: 10000
write_request_timeout_in_ms: 10000
truncate_request_timeout_in_ms: 60000
request_timeout_in_ms: 10000
cross_node_timeout: false
endpoint_snitch: Ec2Snitch
dynamic_snitch_update_interval_in_ms: 100
dynamic_snitch_reset_interval_in_ms: 600000
dynamic_snitch_badness_threshold: 0.1
request_scheduler: org.apache.cassandra.scheduler.NoScheduler
index_interval: 128
server_encryption_options:
internode_encryption: none
keystore: conf/.keystore
keystore_password: cassandra
truststore: conf/.truststore
truststore_password: cassandra
client_encryption_options:
enabled: false
keystore: conf/.keystore
keystore_password: cassandra
internode_compression: all
I think http://www.datastax.com/documentation/cassandra/1.2/cassandra/dml/dml_config_consistency_c.html will clear up a lot of this. In particular, QUORUM/ONE is not guaranteed to return the most recent data. QUORUM/QUORUM is. So is ALL/ONE, but that will be intolerant to failure on write.
Edit to go with the new information:
CassandraHostRetryService is part of Hector. I assumed you were testing with cqlsh like a sane person would. Lessons:
Use cqlsh for testing
Use the DataStax Java Driver for building your application, which is faster, easier to use, and has more insight into the cluster state than Hector thanks to the native protocol it's built on.
I have the cassandra cluster of 12 nodes on EC2.
Because of some failure we lost one of the node completely.I mean that machine do not exist anymore.
So i have created the new EC2 instance with different ip and same token as that of the dead node and i also had the backup of data on that node so it works fine
But the problem is the dead nodes ip still appears as a unreachable node in describe cluster.
As that node (EC2 instance) does not exist anymore I can not use the nodetool decommission or nodetool disablegossip
How can i get rid of this unreachable node
I had the same problem and I resolved it with removenode, which does not require you to find and change the node token.
First, get the node UUID:
nodetool status
DN 192.168.56.201 ? 256 13.1% 4fa4d101-d8d2-4de6-9ad7-a487e165c4ac r1
DN 192.168.56.202 ? 256 12.6% e11d219a-0b65-461e-babc-6485343568f8 r1
UN 192.168.2.91 156.04 KB 256 12.4% e1a33ed4-d613-47a6-8b3b-325650a2bbd4 RAC1
UN 192.168.2.92 156.22 KB 256 13.6% 3a4a086c-36a6-4d69-8b61-864ff37d03c9 RAC1
UN 192.168.2.93 149.6 KB 256 11.3% 20decc72-8d0a-4c3b-8804-cc8bc98fa9e8 RAC1
As you can see the .201 and .202 are dead and on a different network. These have been changed to .91 and .92 without proper decommissioning and recommissioning. I was working on installing the network and made a few mistakes...
Second, remove the .201 with the following command:
nodetool removenode 4fa4d101-d8d2-4de6-9ad7-a487e165c4ac
(in older versions it was nodetool remove ...)
But just like for the nodetool removetoken ..., it blocks... (see comment by samarth in psandord answer) However, it has a side effect, it puts that UUID in a list of nodes to be removed. So next we can force the removal with:
nodetool removenode force
(in older versions it was nodetool remove ...)
Now the node accepts the command it tells me that it is removing the invalid entry:
RemovalStatus: Removing token (-9136982325337481102). Waiting for replication confirmation from [/192.168.2.91,/192.168.2.92].
We also see that it communicates with the two other nodes that are up and thus it takes a little time, but it is still quite fast.
Next a nodetool status does not show the .201 node. I repeat with .202 and now the status is clean.
After that you may also want to run a cleanup as mentioned in psanford answer:
nodetool cleanup
The cleanup should be run on all nodes, one by one, to make sure the change is fully taken in account.
Normally when replacing a node you want to set the new node's token to (failure node's token) - 1 and let it bootstrap. As of 1.0 there is now a flag you can specify on startup to replace a dead node: "cassandra.replace_token=".
Since you have already added the new node with the same token there's an extra step:
Move the new node's token to (failure node's token) - 1 using nodetool move
Run nodetool removetoken <failed node's token> from one of the up nodes
Run nodetool cleanup on each node
These are basically the pre 1.0 instructions for replacing a dead node with the additional token move.