fingerprint: don't clear Consul/Vault attributes on failure #14673
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Clients periodically fingerprint Vault and Consul to ensure the server has updated attributes in the client's fingerprint. If the client can't reach Vault/Consul, the fingerprinter clears the attributes and requires a node update. Although this seems like correct behavior so that we can detect intentional removal of Vault/Consul access, it has two serious failure modes: (1) If a local Consul agent is restarted to pick up configuration changes and the client happens to fingerprint at that moment, the client will update its fingerprint and result in evaluations for all its jobs and all the system jobs in the cluster. (2) If a client loses Vault connectivity, the same thing happens. But the consequences are much worse in the Vault case because Vault is not run as a local agent, so Vault connectivity failures are highly correlated across the entire cluster. A 15 second Vault outage will cause a new `node-update` evalution for every system job on the cluster times the number of nodes, plus one `node-update` evaluation for every non-system job on each node. On large clusters of 1000s of nodes, we've seen this create a large backlog of evaluations. This changeset updates the fingerprinting behavior to keep the last fingerprint if Consul or Vault queries fail. This prevents a storm of evaluations at the cost of requiring a client restart if Consul or Vault is intentionally removed from the client.
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shoenig
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Sep 23, 2022
schmichael
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Extension of #14673 Once Vault is initially fingerprinted, extend the period since changes should be infrequent and the fingerprint is relatively expensive since it is contacting a central Vault server. Also move the period timer reset *after* the fingerprint. This is similar to #9435 where the idea is to ensure the retry period starts *after* the operation is attempted. 15s will be the *minimum* time between fingerprints now instead of the *maximum* time between fingerprints. In the case of Vault fingerprinting, the original behavior might cause the following: 1. Timer is reset to 15s 2. Fingerprint takes 16s 3. Timer has already elapsed so we immediately Fingerprint again Even if fingerprinting Vault only takes a few seconds, that may very well be due to excessive load and backing off our fingerprints is desirable. The new bevahior ensures we always wait at least 15s between fingerprint attempts and should allow some natural jittering based on server load and network latency.
schmichael
added a commit
that referenced
this pull request
Sep 26, 2022
Extension of #14673 Once Vault is initially fingerprinted, extend the period since changes should be infrequent and the fingerprint is relatively expensive since it is contacting a central Vault server. Also move the period timer reset *after* the fingerprint. This is similar to #9435 where the idea is to ensure the retry period starts *after* the operation is attempted. 15s will be the *minimum* time between fingerprints now instead of the *maximum* time between fingerprints. In the case of Vault fingerprinting, the original behavior might cause the following: 1. Timer is reset to 15s 2. Fingerprint takes 16s 3. Timer has already elapsed so we immediately Fingerprint again Even if fingerprinting Vault only takes a few seconds, that may very well be due to excessive load and backing off our fingerprints is desirable. The new bevahior ensures we always wait at least 15s between fingerprint attempts and should allow some natural jittering based on server load and network latency.
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Clients periodically fingerprint Vault and Consul to ensure the server has updated attributes in the client's fingerprint. If the client can't reach Vault/Consul, the fingerprinter clears the attributes and requires a node update. Although this seems like correct behavior so that we can detect intentional removal of Vault/Consul access, it has two serious failure modes:
(1) If a local Consul agent is restarted to pick up configuration changes and the client happens to fingerprint at that moment, the client will update its fingerprint and result in evaluations for all its jobs and all the system jobs in the cluster.
(2) If a client loses Vault connectivity, the same thing happens. But the consequences are much worse in the Vault case because Vault is not run as a local agent, so Vault connectivity failures are highly correlated across the entire cluster. A 15 second Vault outage will cause a new
node-updateevalution for every system job on the cluster times the number of nodes, plus onenode-updateevaluation for every non-system job on each node. On large clusters of 1000s of nodes, we've seen this create a large backlog of no-op evaluations. (See also #14621 for mitigations of this.)This changeset updates the fingerprinting behavior to keep the last fingerprint if Consul or Vault queries fail. This prevents a storm of evaluations at the cost of requiring a client restart if Consul or Vault is intentionally removed from the client.