§2024-05-31

GPT,

In MongoDB replication logs, there are several key phrases and messages that you should pay attention to in order to monitor the health and status of your replication setup. Here are some of the critical phrases and what they indicate:

• "PRIMARY": Indicates which node is currently the primary in the replica set.
• "SECONDARY": Indicates nodes that are currently secondaries in the replica set.
• "RECOVERING": Nodes that are recovering and not yet available for reads.
• "STARTUP": Nodes that are in the process of starting up.
• "ROLLBACK": Indicates that a node is rolling back operations to achieve consistency with the primary.
• "RESYNCING": Indicates that a secondary is resyncing from the primary.
• "heartbeat": Messages related to heartbeats between replica set members, which are critical for determining the state of each node.
• "election": Messages related to elections for primary. Look for messages indicating the start and end of an election.
• "sync source": Indicates which node a secondary is syncing from. Pay attention to changes in sync source.
• "initial sync": Indicates an initial synchronization process.
• "vote": Messages related to voting during an election process.
• "Term changed": Indicates a change in the term, which is important in elections.
• "cannot connect" or "failed to connect": Issues connecting to other replica set members.
• "Stepping down": Indicates that a primary node is stepping down to become a secondary.
• "replSet": General prefix for many replication-related logs. Messages with this prefix often indicate important state changes or issues.
• "replication lag": Indicates delays in replication, which can be a critical issue for data consistency and availability.

To write a filter clause in syslog-ng to catch specific phrases in MongoDB replication logs, you need to use the filter function to match log messages containing these phrases. You can combine multiple filter conditions using the or operator.

Here’s an example of how you can configure a filter in syslog-ng to catch the mentioned phrases:

filter f_mongodb_replication {
    match("PRIMARY" value("MESSAGE")) or
    match("SECONDARY" value("MESSAGE")) or
    match("RECOVERING" value("MESSAGE")) or
    match("STARTUP" value("MESSAGE")) or
    match("ROLLBACK" value("MESSAGE")) or
    match("RESYNCING" value("MESSAGE")) or
    match("heartbeat" value("MESSAGE")) or
    match("election" value("MESSAGE")) or
    match("sync source" value("MESSAGE")) or
    match("initial sync" value("MESSAGE")) or
    match("vote" value("MESSAGE")) or
    match("Term changed" value("MESSAGE")) or
    match("cannot connect" value("MESSAGE")) or
    match("failed to connect" value("MESSAGE")) or
    match("Stepping down" value("MESSAGE")) or
    match("replSet" value("MESSAGE")) or
    match("replication lag" value("MESSAGE"));
};

log {
    source(s_mongo);   # Source definition for MongoDB logs
    filter(f_mongodb_replication);
    destination(d_mongo_filtered_logs);  # Destination definition for filtered logs
};

Why Use value("MESSAGE")?

Specificity: By specifying value("MESSAGE"), you ensure that only the content part of the log message is checked, not metadata such as timestamps or hostnames.

Clarity: It makes the filter definition explicit and clear, indicating precisely what part of the log entry you are interested in. Practical Example

If a MongoDB log entry is:

2024-05-30T12:00:00.000+0000 I REPL [replSet] PRIMARY [member:2] elected primary

The value("MESSAGE") refers to:

PRIMARY [member:2] elected primary

• in match("PRIMARY" value("MESSAGE")) how to make it case insensitive so that it will match primary

In syslog-ng, you can make the match function case-insensitive by using the flags() parameter with the icase flag. This tells syslog-ng to perform a case-insensitive match.

Here's how you can modify the filter clause to make it case-insensitive:

filter f_mongodb_replication {
    match("PRIMARY" value("MESSAGE") flags("icase")) or
    match("SECONDARY" value("MESSAGE") flags("icase")) or
    match("RECOVERING" value("MESSAGE") flags("icase")) or
    match("STARTUP" value("MESSAGE") flags("icase")) or
    match("ROLLBACK" value("MESSAGE") flags("icase")) or
    match("RESYNCING" value("MESSAGE") flags("icase")) or
    match("heartbeat" value("MESSAGE") flags("icase")) or
    match("election" value("MESSAGE") flags("icase")) or
    match("sync source" value("MESSAGE") flags("icase")) or
    match("initial sync" value("MESSAGE") flags("icase")) or
    match("vote" value("MESSAGE") flags("icase")) or
    match("Term changed" value("MESSAGE") flags("icase")) or
    match("cannot connect" value("MESSAGE") flags("icase")) or
    match("failed to connect" value("MESSAGE") flags("icase")) or
    match("Stepping down" value("MESSAGE") flags("icase")) or
    match("replSet" value("MESSAGE") flags("icase")) or
    match("replication lag" value("MESSAGE") flags("icase"));
};

source s_mongo {
    file("/path/to/mongodb/logfile");
};

destination d_mongo_filtered_logs {
    file("/path/to/filtered/logs");
};

filter f_mongodb_replication {
    match("PRIMARY" value("MESSAGE") flags("icase")) or
    match("SECONDARY" value("MESSAGE") flags("icase")) or
    match("RECOVERING" value("MESSAGE") flags("icase")) or
    match("STARTUP" value("MESSAGE") flags("icase")) or
    match("ROLLBACK" value("MESSAGE") flags("icase")) or
    match("RESYNCING" value("MESSAGE") flags("icase")) or
    match("heartbeat" value("MESSAGE") flags("icase")) or
    match("election" value("MESSAGE") flags("icase")) or
    match("sync source" value("MESSAGE") flags("icase")) or
    match("initial sync" value("MESSAGE") flags("icase")) or
    match("vote" value("MESSAGE") flags("icase")) or
    match("Term changed" value("MESSAGE") flags("icase")) or
    match("cannot connect" value("MESSAGE") flags("icase")) or
    match("failed to connect" value("MESSAGE") flags("icase")) or
    match("Stepping down" value("MESSAGE") flags("icase")) or
    match("replSet" value("MESSAGE") flags("icase")) or
    match("replication lag" value("MESSAGE") flags("icase"));
};

log {
    source(s_mongo);
    filter(f_mongodb_replication);
    destination(d_mongo_filtered_logs);
};